Popular Science Monthly/Volume 18/February 1881/Popular Miscellany
The Age of the Trenton Gravels.—The age of the gravel in which flint implements have been found at Trenton, New Jersey, is carefully discussed by Mr. Henry-Carvill Lewis, in a paper read by him before the Academy of Natural Sciences of Philadelphia. Mr. Lewis divides the surface formations of southeastern Pennsylvania into five clays and four gravels, of which nine deposits the Trenton gravel, as he calls the implement-bearing formation, is, except the recent alluvium, the most recent. At Philadelphia it is called the river-gravel and sand, and contains pebbles which are made exclusively from the rocks forming the upper valley of the Delaware River, and which have the flat shape characteristic of all true river-gravels. It is confined to the immediate vicinity of the river, and has been traced as far up as the Water-Gap. Through-out its whole course it lies within a channel previously excavated through the bowlder-bearing Philadelphia brick-clay and its red gravel, which have been shown to belong to the Champlain epoch. It is therefore later than those formations. The deposit is spread out to its greatest extent at Trenton, where the long, narrow valley of the Delaware, with its precipitous banks and continuous downward slope, opens out into the wide, alluvial plain at a lower level. The fluvia-tile character of this gravel is shown by evidence of various characters, as by the exposures of the "flow-and-plunge structure," in which the layers are seen to dip up-stream, as would be expected to result from the action of downward-flowing water, while the tertiary gravels show in their layers, dipping southeast, evidence of their deposition by incoming oceanic tides. It frequently, also, instead of lying in a flat plain, forms banks with a higher ground close to the present river-channel, and sloping down toward the ancient bank, as often takes place according to the laws of river deposits. The formation can not, however, have been made under the operation of any such flood as has been known within the historical epoch, for no such flood has supplied the amount of water which would be required. It also bears marks of ice-action. It may then be ascribed to a glacier; not to the great glacier of the glacial period, for that glacier at its melting deposited the much older brick-clay and red gravel, but to another more recent glacier whose flood flowed through a channel excavated in the deposits of the first glacial period. This second glacier was much smaller than the first, had its southern extremity confined to the valley, and probably corresponded with the age which European geologists style the Reindeer period. From the fact that the palœoliths found here are similar to the stone implements found among the Esquimaux, Mr. Lewis thinks that they may be the relics of an Esquimau race who once lived in the valley, and he suggests the Esquimau period as a suitable name for their age. Finally, he sums up his conclusions as follows: "1. That the Trenton gravel, the only gravel in which implements occur, is a true river deposit of post-glacial ago, and the most recent of all the gravels of the Del- aware Valley. 2. That the palajoHths found in it really belong to and are a part of the gravel, and that they indicate the existence of man in a rude state at a time when the flooded rivci" flowed on top of this gravel. 3. That the data do not necessarily prove, geologically considered, an extreme antiquity of man in Eastern America."
Prehistoric Mining in North Carolina.
Mining for mica has become a profitable pursuit in North Carolina. It is a curious fact that the best mines are located upon sites which afford evidence of having been worked in prehistoric times, and are called there "old diggings." Most of the old works probably belonged to the mound- builders, but a tradition coming down from the Indians ascribes some of them to white men. The tradition has recently been con- firmed by the discovery of old implements of iron in a prehistoric shaft in Macon County, which are fully described and fig- ured by Mr. F. W. Simonds, in the " Ameri- can Naturalist." The implements were found in the rubbish which had accumu- lated within the shaft, between thirty-five and fifty feet below the surface, and consist of an axe of a pattern now rarely met with, light in weight, and having on the blade a brand which has been nearly effaced by erosion; two articles which were evidently gudgeons of a windlass, with heads pronged for the insertion of levers, pointed at the ends, so that they could be driven into a wooden roller, and having the lower part of the shank squared to prevent their turning in the wood, and the upper part round so as to serve as an axle for the roller; and a wedge with battered head. All were of wrought iron, and had probably been worn out and thrown away. Mr. Simonds sug- gests that they are the relics of a party of Spaniards who left one of the ancient colo- nies or expeditions on a " prospecting tour " and tried the mines. Less palpable evi- dences of more skillful mining than that of any aborigines have been found in other shafts.
The Great Glacier of the Yellowstone.
Professor Archibald Geikie, Director of the Geological Survey of Scotland, gives in I
the " American Naturalist " an interesting notice, based on his personal observations, of the ancient glaciers of the Kocky Moun- tains. He refers to the absence of signs of glacial action in the region between the Missouri Valley and the Sierra Nevada, which has been mentioned by American geologists, and regards it as the result chiefly of meteorological conditions. Then, having spoken well of the accounts given of the glaciers of the mountains by our geologists, he records his own observations of them. Entering the Yellowstone Valley from Fort Ellis, a little above the first canon, he observed a prominent rock like a cottage, and weighing more than a hundred and fifty tons, lying, like other smaller errat- ics around it, on crescent-shaped mounds moraine-heaps in the midst of the alluvial plain. The broad valley was full of moraine- stuff. Here, he observes, was a great gla- cier moving northward, "while in British Columbia, on a parallel only about two hundred and fifty miles farther north, there was a massive ice-sheet moving southward. It will be a point of no little interest to trace these two converging ice-streams to- ward each other." In ascending the Yel- lowstone Valley toward the National Park, scattered moraine - mounds and abundant transported blocks continue to denote the course and size of the former glacier. The intense glaciation of the second cafion was a surprise. The rocky knobs at the lower entrance of the great ravine were as per- fectly smooth, polished, and striated as the rocks at the margin of any Swiss or Nor- wegian glacier, and the steep sides of the canon had been ground and striated in the same way, to the height of certainly not less than eight hundred feet. Above the second canon the moraine - heaps become more abundant and tumultuous, here and there inclosing small lakes; and they were found also, with erratics, in the tributary valley's. The trail from the Mammoth Springs by Blacktail Deer Creek, over to the Yellow- stone, leads across mounds of glacial dihris among which huge bowlders of granite and granitoid gneiss are conspicuous. Some parts of the route present long, smooth slopes, dotted with bowlders precisely like some Scottish bowlder-clay moors. These signs of glaciation can be traced up to and across the water-shed leading over to the Yellowstone Valley, and " they prove beyond question that not only was that valley filled up with ice, but that the glacier plowed over the ridge one thousand feet above the valley-bottom and passed into the country lying to the westward." Professor Geikie made an estimate of the thickness of the ice, from the indications afforded by the position of the highest erratics which he observed on the slopes of Mount Washburn, from which he concludes that it could not have been less than sixteen hundred and fifty, and was probably at least nineteen hundred feet. It is clear to him, from all the evidence, that the ice of the Yellowstone Valley was more than that of a more local or valley glacier. It was massive enough to fill up the main valley and override the surrounding hills, crossing minor water- sheds and spreading into adjacent drainage basins; and he believes it may be eventu- ally shown that the snow-fields of the Wind River and Teton ranges were so extensive that their ice-rivers streamed northward across the buried water-shed, and poured into the Yellowstone. An exploration of the country lying in the Yellowstone Valley, northward into the area of northern glacia- tion within the British line, is desirable to show whether there was any connection between the glaciers of the Rocky Moun- tains and the great northern ice-sheet, and whether the latter, as it moved dawn the valley of the Missouri, was swelled by the accession of ice-streams from the moun- tains.
Structural Peculiarities of the Ed.
Frank Buckland gives an interesting descrip- tion of the curious yet simple apparatus by means of which the eel is able to keep his gills moist without taking in fresh water, and thereby to live a long time out of water and travel on land for a considerable dis- tance. Close to the pectoral fin of the eel is a slit which acts as a valve, connecting with a large cavity inside of which are the gills. This cavity the eel has the power of filling with water, and of keeping within it a supply which prevents the gill-fibers from adhering together so as to stop respiration. It is surrounded by a loose membrane, and is filled and emptied by means of a curious
bit of mechanism which is thus described: "A framework of very delicate bones, each bone connected with its neighbor by an clas- tic membrane of the consistency of gold- beater's-skin, forms a fan-shaped covering over the gills; its action is very like, if not the same as, the action of an umbrella. When the eel wishes to take in his water- supply, he, as it were, opens his umbrella- shaped framework and fills his reservoir; when he wishes to expel the water, he, as it were, closes his umbrella." When an eel is taken out of the water he will soon expand his reservoir, and swellings will appear on either side of his head. He will shortly wish to refill his reservoir, and, if given water, will immediately take in a considerable quantity. With this he is ready to take an overland journey if he wishes to change his abode. The eye of the eel is protected against the mud, stones, etc., among which he lives by what Mr. Buckland calls a wonderful specta- cle or eye-glass, formed by the conversion of the skin of the head where it passes over the eye into a thin but strong transparent membrane, which forms an admirable guard against injury.
Spilt Stones in the Desert. Those parts of the desert of Sahara called the Hamadas which are also among the most desolate tracts of the region are strewed with sili- cious pebbles which are all broken up, pre- senting sharp edges, as if they had just been split with a hammer. Sometimes frag- ments of these pebbles could be found lying together with their fractured sides facing each other and fitting perfectly when brought close together. The phenomenon has baffled explanation for a long time. M. J. Brun has recently communicated to the Scientific Society of Geneva his conclusion that it is the result of a curious combination of chem- ical and mechanical actions. He found by analysis that the sand of the desert was com- posed of quartz, gypsum, and marl, with traces of salt. The quartz-grains act under the influence of the solar rays as burning- lenses upon the gypsum, and render it an- hydrous. The sand and fine anhydrous gyp- sum-dust are driven about by the winds and cover all the stones; the dust penetrates the little cracks in the stones, when it is wet by the dews, and swells. With continuous accessions of gypsum and repeated heavy dews the accumulatiou of plaster goes on increas- ing, the cracks are enlarged, and in time the stone is split.
Variations in the Forms of Water-PIants.
Dr. W. Bchrens, of Brunswick, has pub- lished a preliminary report of researches which he has been making into the influence of the movement, and other physical rela- tions, of water upon the plants growing in it. He observes that water-plants, both those that grow submerged and those which appear on the surface, are subject to a va- riety of modifications in the forms of their stems, leaves, and other organs, according as the water in which they grow is in more or less lively motion. Plants which grow in a stream, and are rooted in the ground, seem to receive a kind of pull from the moving force of the water, which is propor- tioned to the speed of the current. If plants which grow indifferently in standing, mod- erately moving, and swift waters, exhibit variations which are constant for the same kind of waters, the conclusion is allowable that the variations are produced by the ki- netic influence of the waters. Plants which are met in only one kind of waters do not exhibit equivalent variations. The common frogbit, of Europe, which floats on the sur- face of still waters, has its leaves always of the same broad kidney-form. The pond- weed, which grows both in still and rnnning waters, exhibits, on the other hand, mani- fold variations. The most common form has floating, oval leaves, the diameters of which are to each other as 1 to Vo. The leaves of those varieties that grow in run- ning water are longer and narrower in pro- portion to the swiftness of the stream; and one form is mentioned in which the diame- ters of the leaves are as 1 to 3. The wa- ter-ranunculuses (Batrachium) afford excel- lent examples of the influence of running water on the forms of plants. Several spe- cies are found in all kinds of waters, the most of them having leaves of two forms, peltate floating leaves, and much divided submerged leaves. They grow in still and running, fresh and brackish waters, and even on the land after the water has dried away. Of the species common in Europe, Batrachium aquatile is the most interesting
object of study in respect to its variations. Its forms are numerous, but they may be ar- ranged under two general heads. The first includes those varieties which have plain floating leaves and also divided, submerged leaves, and the second those which have only divided leaves under water. The forms of the former class occur principally in waters having little motion; the floating leaves are round and peltate, with fine slight scallops on the borders. In swifter waters the leaves are cut up into pointed lobes, the distinctness of which increases with the speed of the current. Dr. Behrens has dis- tinguished about thirty varieties in different waters, most of which he has described and named in his paper. In the swiftest cur- rents, the floating leaves disappear, and only the varieties of the second form those hav- ing exclusively divided, submerged leaves are found. Still another change comes over the Batrachium when the water is taken away from it. It grows up with a short stem, and is thickly covered with gceen leaves divided into numerous short, firm, succulent lobes. Dr. Behrens is preparing a work in which variations of this sort will be fully discussed, with illustrations.
Progress in Photograpliv. "Some Re- cent Advances in Photography " is the sub- ject of a paper recently read before the Society of Arts by Captain Abney, R. E., F. R. S., in which reference was made to the more important improvements in the art that have been put in practice since 1875. A new negative process, called the gelatino-bromide process, offers decided ad- vantages. It consists in the use of a gelatine emulsion of silver bromide for the sensitive surface. With a plate thus pre- pared, a photograph may now be taken in one second of time which it formerly took thirty seconds to secure; and a plate can be prepared which needs an exposure of only one sixtieth of a second, when a view is fairly lighted to secure a soft and harmoni- ous negative. It makes instantaneous views possible under cii'cumstances which were im- possible, in illustration of which the speaker exhibited a view in which the shadow and reflection of a swallow passing in the air over a pond were perfectly represented. The plates and the development of pictures taken by this process are perfectly clean. The plates, moreover, have the quality of preserving the impressed image for a long time after they have been exposed and be- fore it has been developed. The chief dis- advantage of the process is that the photog- rapher using it has very little power to give local intensity to his picture. Till lately, a red light had to be employed in the devel- oping-room, and this was painful to the op- erator. The difficulty has been obviated by adding iodide of silver to the emulsion in the proportion of one part of iodide to eight of the bromide, when an orange light can be used with impunity, and the shadows are given a wonderful clearness. When a collodion emulsion is adapted to a flexible support and used for the negatives, the op- erator is able to do away with glass and its weight, and may store rolls of sensitive ma- terial in the camera itself. Then, by turn- ing a screw, he may place fresh portions of the band in a condition for exposure. After exposure, paper prepared with this emulsion may be moistened with turpentine, and the film bearing the image, almost free from weight and bulk, may be stripped off. To print from these flimsy negatives, it is only necessary to place them on glass. When a flexible support shall have been introduced for the gelatine emulsion, the negative pro- cesses of photography will be almost per- fect. With the collodion emulsion, we are able to get a physical condition of the bro- mide, in which it will answer to the vibra- tion of the rays of the lowest refrangibility. Photographs of the solar spectrum taken on this salt were shown, corresponding to wave- lengths which lie more than three times as far below the red as the distance of the visi- ble spectrum. This process is being applied to the examination of different colorless bodies, with a view of obtaining spectro- scopic analyses of them. It has been dis- covered that the photographic image is ren- dered undevelopable by the action of oxid- izing agents, and this alike whether it be produced on a collodion or a gelatine film or on paper. The oxidation of the image goes on also in ordinary atmospheric condi- tions, more especially under the influence of light, and in it we have a simple explanation of what is known as solarization. A plati- num process, in which an image is produced
in platinum-black, is about four times as sensitive as the ordinary silver process, and marks the greatest advance in printing that has been made for many years. Another printing process is based on the reduction, by ferrous oxalate, of bromide of silver which has been exposed to light, and was discovered almost simultaneously by Mr. Willis, of England, and Mr. Carey Lea, of Philadelphia. The prints obtained by this process have great permanence, since no or- ganic compound of silver, the great agent of deterioration, is present in them. Mr. Lea has discovered within the last year that the power of development which is shared by most of the organic salts of ferrous oxide is not limited to them, but is possessed also by many of its inorganic compounds. He gives a brief account of his researches in this direction, and of the properties of the different salts of the oxide, in the " Ameri- can Journal of Science " for June.
The Regnlation of Visnal Tests. The
Boston "Herald" published last summer a review of what had been done in the United States during the previous twelve months to secure protection against the dangers arising from color-blindness and visual de- fects in seamen, railroad-men, and other persons occupying positions of trust in which the quality of eyesight is important. Three departments of the national Gov- ernment have adopted regulations on the subject. The War Department has or- dered the examination of recruits by test- cards, to test their power of distinguishing objects at a distance, and with worsteds for their perception of colors. The Treasury Department has made the examination of all pilots, as to their ability to distinguish colors, compulsory, with the provision that "a second visual examination will not be re- quired in any case." The Navy Department has ordered a similar examination for all persons in the navy, or who may hereafter enter it. The House Committee on Naval Affairs has reported favorably on a petition of Dr. B. Joy Jeffries and others for the en- actment of a general law of control for the naval -and merchant service, and for a rep- resentation of the United States in an Jn- ternational Congress to agree upon definite standards of color-tests, and has reported a bill authorizing such representation, which will come up at the next session of Congress. One steamboat company and one railroad company have instituted a compulsory ex- amination of all their men. -The State of Connecticut has adopted a law for the ex- amination of railroad-men, with the follow- ing requirements for a certificate in thg first class (engineers, firemen, and brakemen): 1. Healthy eyes and eyelids without ha- bitual congestion or inflammation; 2. Un- obstructed visual field; 3. Normal visual acuteness; 4. Freedom from color-blindness; 5. Entire absence of cataract or other pro- gressive disease of the eye. For second- class certificates (conductors, station-agents, switchmen, etc.) the first two conditions are the same, but in the third condition is re- quired only " visual acuteness at least equal to three fifths without glasses and normal with glasses in one eye and at least one half in the other eye, with glasses," and in the fourth " freedom from color-blindness in one eye, and color-perception at least equal to three quarters in the other eye."
Form of the Ligbtnin^-Rod. The sub- ject of the proper form of lightning-conduct- ors, long a disputed one among scientific men, has recently been experimentally in- vestigated by Mr. W. H. Preece, with the i'csult of confirming the position of Faraday, that the section of a rod is the essential ele- ment. The advocates of rods of large sur- face, such as ribbons, tubes, etc., among whom was the late Professor Henry, con- clude, from the fact that static electricity resides upon the surface, that electricity of high tension, such as a lightning-discharge, is better conducted away by a large extent of surface. Mr. Preece stated that no direct experiments had, so far as he was aware, ever been made to settle the question, which was an important one, as the acceptance of the surface theory had led to the employ- ment of unsightly and costly conductors, when a simple rod would answer all pur- poses. The experiments were made in the laboratory of Dr. Warren de la Rue, and had the advantage of his advice and assist- ance. In the first experiment copper con- ductors thirty feet in length, in the form of a solid rod, a thin tube, and ribbon, each of precisely the same mass, were used. The
electricity was obtained from 3,240 ehloride- of-silver cells, and accumulated in a con- denser of a capacity of 42'8 micro-farads. The sudden discharge of this quantity of electricity produced results similar in char- acter to lightning. It was capable of com- pletely deflagrating 2^ inches of platinum wire of .0125 inch diameter, and of raising to diiferent degrees of incandescence greater lengths. Such wire, afiixed to a white card so as to record the effect, was used to measure the discharge after it had passed through the conductor. Each form of conductor gave ex- actly the same result in the deflagration and heating of the platinum, showing that differ- ent extents of surface had no effect. As it might be thought that, in copper conductors of such length as those used, differences in conductivity could not be readily detected, the experiments were repeated with lead conductors, the resistances of which were twelve times that of copper, with the same results. An experiment, to determine how closely variations in the discharge could be estimated, showed that a change of resist- ance of five per cent, could have been easily detected. 5Ir. Preece, therefore, concludes that no more effective lightning-conductor than a simple rod or wire rope can be de- vised.
The Phenomena of Thnnderstormsi
In a recent lecture at Glasgow, Professor Tait reviewed the present state of our knowledge of thunderstorms, and pointed out the chief conditions upon which the phe- nomena seemed to depend. The different degrees of conductivity of the air to which the zigzag form of the flash is due he thought might be produced by local electri- fication, which would have the same effect as heat in rarefying the air and making it a better conductor. Sheet-lightning is proba- bly the reflection of a flash of forked light- ning, itself invisible to the observer. Sum- mer lightning is, in some cases, of a similar character, but in others, when the sky is clear, it seems to be due to discharges taking place in an upper strata of the atmosphere, the thunder being inaudible both on account of the distance and its originating in an at- mosphere of but small density. The dis- charge in the form of a luminous ball is of rare occurrence, and but little is known of it. It is probably a natural form of Leyden jar very highly charged. The light of a tiash, Professor Tait states, is of very much greater intensity than is commonly sup- posed, the apparent brightness being, on account of the exceeding small duration, less than one hundred thousandth part of what it would be if the lightning were permanent. This duration is not more than the millionth part of a second, and hence it is a mistake to suppose that you can sec the direction in which the discharge is passing, whether from the clouds to the earth or from the earth to the clouds. Pro- fessor Tait insists upon the necessity of properly pointing and grounding lightning- rods to secure safety, and mentions several instances of the ignorance in this matter which seems to prevail among even well- educated people. In one case the point of the rod was actually covered with a glass insulator. The best ground connection is with the water-mains, but large masses of metal or other conductor in a moist soil an- swer when these are not at hand. Connec- tion with a body of water inclosed in a ma- sonry basin, such as a reservoir, is not a proper way of grounding the rod. A light- ning-rod acts as a constant drain upon the charge in the clouds in its neighborhood, and when the rods are numerous over any area, as in a well-protected town, storm- clouds will pass over without any lightning- flashes taking place, though such form of discharge will occur before reaching the protected district and after passing it. The lecturer insisted that people should regard the use of rods as both a public and private duty. In regard to the sources of electrici- ty in the atmosphere. Professor Tait has been led by experimental researches to in- fer that a separation of the opposite elec- tricities occurs simply by the contact of particles of air and aqueous vapor, which, on the kinetic theory of gases, are in con- stant collision. In the same way zinc and copper become oppositely electrified when brought into contact. The precipitation of vapor-particles into cloud-particles and the agglomeration of these into rain-drops enor- mously increase the electrification, as the potential of a free charged sphere is pro- portional directly to the quantity of elec- tricity on it and inversely to its radius. The
separation of these highly charged particles of air and water is effected by gravity and the diffusion of gases which would cause the air-particles to escape from among the mass of precipitated vapor to the less highly electrified air above. Sir William Thomson has offered an explanation of the phenom- ena, based upon the fact that the lower air is usually negatively charged. Ascending currents carrying this air upward, the elec- tricity, which was formerly spread out over a large area, may by convection become so much less diffused that it will be raised to a high enough potential to give a spark. However the electrification of the precipi- tated vapor occurs, there is no question about the fact that, clouds once formed, the particles are electrified. The solution of the problem of just how this is brought about must in all probability come through exper- iments made on a larger scale than any so far conducted in the laboratory.
Science in the Schools of France. The
modifications in the course of studies in the French public schools, recently decreed by the Superior Council, give to scientific teach- ing a more prominent place than has hither- to been allowed it, especially in the element- ary classes. In the seventh class, the ele- ments of the natural history of animals and plants are added to the history of soils and stones, and take the preference over it, as offering more interest to children and being of greater practical utility. In the sixth class, an hour is deducted from the ten de- voted to Latin and added to those given to the sciences, which are allowed four hours a week. In the fifth class, where scientific instruction has been obviously deficient, the hours for Latin are reduced to five, and the sciences are given four hours. In the fourth class an hour is taken from Greek, and the hours for scientific instruction are increased to four. Scientific instruction will be continued in the third, second, and rhe- torical classes without encroaching upon the other courses, an hour being taken from the study-hours for new subjects of natural his- tory in the third class, for physics in the second class, and for subjects of physics which have not been previously entered upon by the pupils, in the rhetorical class. I The Superior Council advises that the teaching of mathematics and the natural sciences in the grammar-classes be committed to spe- cial professors whenever the funds of the school will permit it and suitable teachers can be obtained; otherwise, professors of science in the higher classes may perform the duty for an additional compensation; or, if there is no other way, the ordinary pro- fessor may provisionally give the special in- struction.
M. Fayc's Theory of the Crnst of the Earth. M. Faye has propounded a new theory of the internal structure of the earth, an important feature of which Is that its solid crust is much thicker under the seas than under the continental masses. The oscillations cf the pendulum and the di- rection of the plumb-line are known to be subject to variations in consequence of the neighborhood of a mountain, or even of a hill, calculations based upon which en- abled Maskelyne to determine the density of the globe. When, however, experiments with the plumb-line and pendulum were applied to table-lands and to the grander mountain-ranges, the deviations correspond- ing to the magnitude of the masses which were expected were not shown. The pen- dulum which is sensitive to the presence of the Great Pyramid of Egypt gives no sign of the neighborhood of the Himalayas. Further than this, a real deficiency of at- traction has been observed upon continents, as if there were a great hollow under them; and the failure of mountain-masses to de- flect the pendulum has been actually at- tributed to the existence of cavities in them. On the other hand, when the investigation is transferred to the sea, the weight is found to be too great, and is in excess of what is demanded by theory, as evidently it falls short of it on the continents. Hence, if we suppose that there is a lack of matter under the continents, we must also suppose that there is under the seas an accumulation of it above the average for the whole earth. M. Faye suggests, to account for these con- tradictions, that the cooling of the earth is going on faster and has taken place to a greater depth under the oceans than under the continents. The temperature at 12,000 feet of depth below the sea is a little higher than the freezing-point; at the same depth
under the continental masses it is com- puted to be about 300. The matter is kept at this temperature by the superior strata of earth almost impermeable to heat, and through which the heat that actually escapes is hardly perceptible. The crust of the earth in such a situation can increase in thickness only at the slowest. Under the sea, on the other hand, matter at the same depth is in almost immediate communication with a cold of the freezing-point, and, instead of having some non-conducting strata above it to prevent its escape, the heat is imme- diately absorbed in a cold of polar intensity. A similar difference exists deep in the beds of the submarine rocks, for the water is im- bibed in their pores to a greater depth than in the sub-continental rocks, and the heat is conveyed away from them by the vertical convection of the warmed water rising in them. The more ancient the existing beds of the sea, the greater is the thickness of the crust that supports them as compared with that of the continents.
Trichinosis on a British School-ship.
A remarkable outbreak of trichinosis on the British reformatory school-ship Cornwall has recently been brought to the notice of the Government health boards. Up to the 23d of September last, the health of the boys had for a long time been good, but, between that day and October 23d, forty- three boys were taken sick, falling ill in batches seven on the 23d, two on the 24th of September, sixteen between the 29th of September and the 1st of October, nine between the 3d and 6th, and the rest at intervals. The outbreak was regarded as one of enteric fever, and the general char- acter and progress of the disease seemed to justify the view. No cause, however, likely to produce such an outbreak could be dis- covered. The hygienic condition of the ship was perfect. The inspector turned his at- tention to the food, and found that none of the officers, who were supplied with distinct food from the boys, were attacked. The boys from a particular mess suffered more than the others, and the tendency of the groups of fresh cases to occur on certain days of the week suggested a connection between the attacks and the salt pork that was served out on Mondays. The body of one of the boys who had died was examined, and the microscope showed living trichinae in his muscles, but none of the appearances of enteric fever were discovered. A new cask of salt pork had been opened just before the disease appeared, the meat from which is supposed to have communicated the trichina? to the boys. This view is confirmed by the fact that the disease ceased soon after the use of the pork was stopped. The method of cooking the meat on the vessel seems to have been defective and not sufficiently thorough to insure the beating of the whole mass to the temperature at which the trichinæ are destroyed.
Sensitive Organs of Deep-Sea Animals.—M. O. Grimm has sought to explain how it is that we find in the great depths of seas and lakes animals without eyes, and besides them others in which those organs are highly developed. According to his view, the light received by animals living in these depths is extremely feeble, but is never totally wanting. An adaptation to these special conditions has taken place. With certain crustaceans, the eyes have gained a considerable volume; with others, the eyes tend to disappear and to be replaced by other sensitive organs. In the Niphargus and Onesimus, for instance, the existence has been detected of extremely developed sensitive organs which may be supposed to serve as organs of touch, taste, and smell. Niphargus Caspius has very small eyes, which can hardly be considered as anything but the remains of normal organs, and can hardly be of any use to an animal living at a depth of from thirty-five to ninety fathoms, but it has highly developed organs of smell and touch on its antennæ. The Onesimus, whose eyes are also very rudimentary, have neither on the antennæ nor other parts of the body sensitive organs like those of the Niphargus, or at least such as they have are very little developed; but a close examination will discover, on the external blade of their foot-jaws (maxillipedes), well-constituted organs of sense, although they are hidden and of a very different structure from those of Niphargus. In explanation of this difference in the nature of the sensory organs of genera so nearly related to each other, M. Grimm remarks that the species he has found with organs of sense on their antennæ always live in the water and never go into the mud. The Onesimus, on the other hand, keep constantly in the mud of the bottom and seek their food by digging, as the moles do. Under such conditions, delicate organs of sense on the antennæ would be of no use, and have become nearly obliterated, while the situation has favored the development of organs in a protected position.