Philosophical Transactions/Volume 1/Number 13
|←Number 12|| Philosophical Transactions, Volume 1
Munday, June 4. 1666.
Certain Problems Touching some Points of Navigation.
The line of Artificial Tangents, or the Logarithmical Tangent-line, beginning at 45 deg. and taking every half
degree for a whole one, is found to agree pretty near with the
Meridian-line of the Sea-Charte; they both growing, as it were,
after the same Proportion. But the Table of Meridional degrees
being calculated only to every Sexagesunal minute of a degree,
shews some small difference from the said Logarithmical Tangent-line.
Hence it may be doubted, whether that difference
do not arise from that little errour, which is committed by calculating
the Table of Meridional degrees only to every minute.
Mr. Oughtred in the VI. Chap. of his Navigation, annexed to the Book; entitled, The Circles of Proportion, and the Horizontal In Instrument, &c. mentions an Artifice, by himself discover'd, by which it may be effected, that the small Parts of the Meridian be not one minute (which on the face of the Earth answers to above an English Mile) but the hundred-thousanth, or, if need be, the millionth part of a minute, scarce exceeding one fifteenth part of an Inch: Which thing, he saith, he is able to perform in Tables unto the Radius 10000000; yet nothing at all differing either in their form or manner of working from those that are now commonly in use.
But which way this is to be done, this Author hath not made known to the Publick. And, though such Tables unto the Radius 10000000, had been brought to light, yet would they not be sufficient to prove the identity or sameness of the said two Lines, as to continue the comparison between them as far, as the one of them, videl. the Logarithmically Tangent-line, is already calculated, that is, to Ten places, besides the Charactoristick. Now therefore, if a certain Rule could be produced, by which the Agreement or Disagreement of the said two Lines might be shew'd, not only to that Extent of places, to which that Tangent Line is already calculated, but also to as many more, as the same maybe yet further extended unto, in infinitum usque; surely that rule would not only save us the labour of making Tables unto the Radius 10000000; but also the Helix or Spiral Line of the Ships Course would be reduced to a more precise exactness, than ever was pretended by Him: and this most Noble and Useful Science (as He justly calls it) which is the Bond of most disjunct Countries, and the Consociation of Nations farthest remote, would attain its full lustre and perfection.
Besides, that the same Rule would also discover a far easier way of making Logarithmes, than ever was practised or known; and therefore might serve, when ever there should be occasion, to extend the Logarithmes beyond that number of places, that is already extant.
Moreover such a rule would enable men to draw; the Meridian line geometrically, that is, without Tables or Scales: which indeed might also be done, by letting of the Secants of every whole or half degree, if there were not this Inconvenience in it (which is not in my Rule:z) That a Line composed of so many small parts, would be subject to many errours, especially in a small compass.
The same Rule also will serve, to find the Course and Distance between two Places assigned, as far, as practice shall require it; and that, without any Table of Meridional parts, and yet with as much ease and exactness.
And seeing all these things do depend on the solution of this Question, Whether the Artificial Tangent-line be the true Meridian line? It is therefore, that I undertake, by God's assistance, to resolve the said Question. And to let the world know the readiness and confidence, I have to make good this undertaking, I am willing to lay a Wager against any one or more persons that have a mind to engage, for so much as another Invention of mine (which is of less subtlety, but of far greater benefit to the publick) may be worth to the Inventor.
For, the great advantage, that all Merchants, Mariners, and consequently the Common-wealth, may receive from this other Invention, is, in my judgment, highly valuable; seeing it will oftentimes make a ship fail, though, according to the common way of failing, the wind be quite contrary, and yet as near to the place intended, as if the wind had been favourable: Or, if you will, it will enable one to gain something in the intended way, whether the wind be good or no (except only when you go directly South or North) but the advantage will be most, where there is most need of it, that is, when the Wind is contrary: So that one may very often gain a fifth, fourth, third part, or more of the intended voyage; according as it is longer or shorter, viz. always more in a longer Voyage, where the gain is more considerable, and more welcome; not only by saving Time, but also Victuals, Water, Fuel, Mens health, and so much Room in the ship.
All this, which is here pretended, the Proposer is to make good by the Verdict of some able Men, who also may give a guess, what this latter Invention may be worth to the owner: And for so much, and no more, he will stand engaged again any one or more Persons, that he will and shall resolve the, Question above-mention'd, viz. Whether the Artificial Tangent-line be the true Meridian-line, yea or no? And if he do not, that then he will loose, and transport to the other Party the whole benefit of the last mentioned invention. But if, on the contrary, he do prove or disprove the Identity of the said two lines, to the judgment of some able Mathematicians, That then so much money be paid him by the other Party, as the said Invention was valued.
And, whereas there are often Wagers laid about things that concern the Engagers little or nothing; 'tis thought, that it would concern all Merchants, Mariners, and all Lovers of the common good, rather to lay wagers against one another about Things of this nature, where the Gainer doth gain as well, as if he had laid his wager about something else, and the Looser hath so far the benefit as well as the Gaine, That he seeth thereby promoted the thing, that concerns them both alike.
Now therefore, to the end, that the Looser may have his benefit by it, as well as the Gainer, it would not be amiss, that the condition were made thus, that the latter should grant the moity of his gain to the Proposer; that thereby he might be enabled to bring to light both those, and some other useful inventions, for the Service of Mankind. And to manifest, that it is not for his own interest only, that the Proposer mentions this; he is willing to impart from that moity, so received, the full moity again to any other person within his Majesty's Dominions, who shall first of all give notice of his Undertaking to prove or disprove the said Identity, and perform it accordingly within the space of two Months, to be computed from the present Date. Those that have a mind to engage, may repair to the Printers of these Tracts, where they may know further.
A new Contrivance of Wheel-Barometer, much more easy to be prepare, than that, which is described in the Micrography; imparted by the Author of that Book.
This is only an easy way of applying an Index to any Common Baroscope, whether the Glass be only a Single Cane, or have a round Bolthead at the top. And by the means thereof, the Variation of the Altitude of the Mercurial Cylinder, which at most is hardly three' Inches, may be made as distinguishable, as if it were three Foot, or three Yards, or as much more, as is desired.
The manner hereof is visible enough by Figure I: where A B C represents the Tube, which may be either Blunt, or with a Head, as A B C (by which latter shape, more room is allow'd for any remainder of Air, to expand the better.) This is to be filled with Quick-silver, and inverted as commonly; but into a Vessel of Stagnant Mercury, made after the fashion of I K, that is, having its sides about 3 or 4 inches high, and the Cavity of it equally big both above and below; and if it can be (besides that part, which is fill'd by the end of the Mercurial Tube, that stands in it) of equal capacity with the hollow of the Cane about B: For then the Quicksilver rising as much in the hollow of I, as it descends at B, the difference of the height in the Receiver I, will be just half the usual difference. And if the receiving Vessel I K have a bigger Cavity, the difference will be less, but if less, the difference will be greater: But, whether the difference be hereby made bigger or less, 'tis no great matter, since by the contrivance of the Wheel and Index which is more fully described in the Preface to the Micrograpby the least variation may be made as sensible as is desired, by diminishing the bigness of the Cylinder E, and lengthening the Index F G, according to the Proportion requisite.
An Account of Four Suns, which very lately appear'd in France, and of two Raine-bows, unusually posited, seen in the same Kingdom, somewhat longer agoe.
These Phænomena are thought worthy to be inferred here, for the Speculation of the Curious in those Kingdoms; as they were publisht in the French Journal des Scavans, of May 10. 1666. viz.
The 9th of April of this present year, about half an hour past nine, there appear'd three Circles in the Sky. One of them was very great, a little interrupted, and white every where, without
the mixture of any other colour. It passed through the midst of the Sun's Disk, and was parallel to the Horizon. Its Diameter was above a hundred degrees, and its Center not far from the Zenith.
The Second was much less and defective in some places, having the Colours of a Rainbow, especially in that part, which was within the great Circle. It had the true Sun for its Center.
The Third was less, than the first, but greater than the second; it was not entire, but only an Arch or Portion of a Circle, whose Center was far distant from that of the Sun, and whose circumference did, by its middle, join to that of the lest Circle, intersecting the greatest Circle by its two extreams. In this Circle were discerned also the Colours of a Rainbow, but they were not so strong, as those of the Second.
At the place, where the circumference of this Third Circle did close with that of the Second, there was a great brightness of Rainbow-Colours, mixt together: And at the two extremities, where this Second Circle intersected the First, appear'd two Parhelia's or Mock-suns; which shone very bright, but not so bright, nor were so well defined, as the true Sun. The False Sun, that was towards the South, was bigger, and far more luminous, than that towards the East. Besides those two Parhelia's which were on the two sides of the true Sun, in the intersection of the First and Third Circle, there was also upon the First great Circle, a third Mock-fun, situated to the North, which was less and less bright, than the two others. So that at the same time there were seen Four Suns in the Heavens.
Figure II. will illustrate the Position of this Phænomenon.
A. The Zenith or the Point Vertical of the place of Observation.
R. The true Sun.
S C H N. The great Circle, altogether White, almost parallel to the Horizon, which pass'd through the true Sun's Diske, and upon which were the false suns.
D E B O. A Rain-bow about, the Sun, forming an entire Circle, but interrupted in some places.
H D N. A portion of a Circle, that war Excentrick to the Sun, and greater than the Circle D E B O, which touch'd D E B O, and was confounded with it in the point D.
H N. The two Mock-Suns, in the intersection of the Semicircle H D N, and the Circle S C H N: The midst of which two False-Suns was white and very luminous; and their Extremities; towards, DI were tinged with the Colours of a Rainbow. The False Sun, mark'd N, was fainter than that, which it mark'd H.
C. The Mock-Sun, all white, and far less shining, than the two others.
I. A space very dark betwixt R. and D.
This Appearance is lookft upon as one of the notablest, that can be seen, by reason of the Excentricity of the Circle H D N,
and because that the Parhelia * * Those Five Suns, that appear'd the 29 March, A. 1629. at Rome, between 2 or 3 of the Clock, in the afternoon, were thus posited; that the two of them, which were in the intersection of two Circles, appear'd in that of a Circle, which passed through the Sun's Diske, with another, that was Concentrick to the Sun: as may he be seen in Figure III. borrow'd (for the easier comparing them together) out of Des-Cartes his Meteors, cap. X. were not in the Interjection of the Circle D E B O with the great Circle S C H N, but in that of the Semi-circle H D N.
As for the two odd Rainbows; they appear'd at Chartres the 10. of August, 1665. about half an hour past six in the Evening; and did cross one another almost at right Angles, as may be seen by Fig. IV.
The Rainbow, which was opposite to the Sun, in the usual manner, was more deeply colour'd, than that, which cross'd it, though even the Colours of the first Iris were not so strong, as they are now and then seen at other times.
The greatest height of the stronger Rainbow, was about 45. degrees; the feebler Rainbow lost one of its Legs, by growing fainter, about 20 degrees above the stronger; and the Leg below appear'd continued to the Horizon.
These Rainbows did not Just decussate one another at right Angles; there was some 6 or 7 degrees difference. The fainter, seem'd to be a Portion of a great Circle; and the stronger was but a Portion of a small Circle, as usually.
The Sun, at their appearance, was about 6 degrees high
above the Horizon, and towards the 17 Azimuth of the West,
The Observer, M. Estienne, notes, that, when he made this Observation, the River of Chartres, which runs very near from South to North, was betwixt him and the Rainbow; and that he stood Level with this River, whence he was distant not above 150 paces: which he adds, that the Curious may the better judge of this Observation.
A Relation of an Accident by Thunder and Lightning, at Oxford.
This was imparted by Dr. Wallis in a Letter, written at Oxford, May 12. 1666. to the Publisher, as follows:
I should scarce have given you so soon the trouble of another Letter, were it not for an Accident which hapn'd here May 10. I had that afternoon, about 4 of the clock heard it thunder at some distance. About 5 of the clock the Thunder coming nearer to us, it began to rain, and soon after (the rain withal increasing) the Thunder grew very loud, and frequent, and with long ratling Claps (though not altogether so great, as I have some other times heard:) and the Lightning with flashes very bright (notwithstanding the clear day-light) and very frequent, (when at the fastest, scarce a full minute between one flash and another; many times not so much, but a second flash before the Thunder of the former was heard:) The Thunder for the most part began to be heard about 8 or 10 second minutes after the flash; as I observ'd for a great part of the time by my Minute-Watch: but once or twice I observ'd it to follow (in a manner) immediately upon it, as it were in the same moment; and the lightning extream red and fiery. I do not use to be much apprehensive of Thunder and Lightning, but I was at this time (I know not well, why ?) very apprehensive, more than ordinary, of mischief to be done by it, for it seem'd to me to be very low and near us (which made me so particular, as to observe the distance of the flash by the noise) and very frequent, and bright, so that, had it been by night as it was by day, it would have been very terrible. And, though I kept within doors, yet I sensibly discover'd a stinking sulphureous smell in the Air. About 7 of the clock it ended, before which time I had news brought me of a Sad Accident upon the water water at Medley about a Mile or somewhat more distant from hence. Two Scholars of Wadham-Colledge, being alone, in a Boat (without a Water-man) having newly thrust off from shore, at Medley, to come homewards, standing near the Head of the Boat, were presently with a stroke of Thunder or Lightning, both struck off out of the Boat into the Water, the one of them stark dead, in whom, though presently taken out of the Water (having been by relation, scarce a minute in it) there was not discerned any appearance of life, sense, or motion: the other was stuck fast in the Mud (with his Feet downwards, and his upper parts above water) like a post not able to help himself out; but, besides a present stonying or numness, had no other hurt; but was for the present so disturb'd in his senses, as that he knew not, how he came there out of the Boat, nor could remember either Thunder or Lightning, that did effect it: and was very feeble and faint upon it; which (though presently put into a warm Bed) he had not thoroughly recover'd by the next Night; and whether since he have or no, I know not.
Others in another Boat, about 10 or 20 yards from these (as by their description I estimate) felt a disturbance and shaking in their Boat, and one of them had his Chair struck from under him, and thrown upon him; but had no hurt. Those immediately made up to the others, and (some leaping into the Water to them) presently drew them either into the Boat or on Shore; yet none of them saw these two fall into the Water (not looking that way) but heard one of them cry out for help presently upon the stroke, and smelt a very strange stinking smell in the Air; which, when I asked him, that told it me, what kind of stink? he faid, like such a smell, as is perceived upon the stricking of Flints together.
He that was dead (when by putting into a warm Bed, and rubbing, and putting strong waters into his Mouth, &c. no life could be brought into him) was the next morning brought to town; where, among multitudes of others, who came to see, Dr. Willis, Dr. Wellington, Dr. Lower, and my self, with some others, went to view the Corps: where we found no wound at all in the skin, the face and neck swart and black, but not more, than might be ordinary, by the settling of the blood: On the right side of the neck was a little blackish spot about an inch long, and about a quarter of an inch broad at the broadest, and was, as if it had been fear'd with a hot iron; and, as I remember, one somewhat bigger on the left side of the neck, below the Ear. Streight down the breast, but towards the left side of it, was a large place about three quarters of a Foot in length, and about two inches in breadth, in some places more, in some less, which was burnt and hard, like Leather burnt with the fire, of a deep blackish red Colour, not much unlike the scorch'd skin of a rosted Pig: And on the fore-part of the left Shoulder such another spot about as big as a Shilling; but that in the neck was blacker and seem'd more fear'd. From the top of the right shoulder, sloping downwards towards that place in his Breast, was a narrow Line of the like scorched skin; as if somewhat had come in there at the neck, and had run down to the breast, and there spread broader.
The buttons of his Doublet were most of them off; which; some thought might have been torn off with the blast, getting in at the neck, and then bursting its way out: for which the greatest presumption was (to me) that, besides 4 or 5 buttons wanting towards the bottom of the Breast, there were about half a dozen together clear off from the bottom of the collar downwards, and I do not remember, that the rest of the buttons did seem to be near worn out, but almost new. The collar of his doublet just over the fore-part of the left shoulder was quit broken asunder, cloth and stiffening, streight downwards, as if cut or chop'd asunder, but with a Blunt tool; only the inward linnen or fustian lineing of it was whole, by which, and by the view of the ragged Edges, it seem'd manifest to me, that it was by a stroak inward (from without) not outwards from within.
His Hat was strangely torn, not just on the Crown, but on the side of the hat, and on the brim. On the side of it was a great hole, more than to put in ones fill through it: some part of it being quite struck away, and from thence divers gashes every way, as if torn, or cut with a Dull tool, and some of them of a good length, almost quite to the edges of the brim. And, beside these, one or two gashes more, which did not communicate with that hole in the side. This also I judged by a stroke inwards; not so much from the view of the edges of those gashes (from which there was scarce any judgment to be made either way) but because cause the lining was not torn, only ript off from the edge of the hat (where it was sow'd on) on that tide, where the hole was made. But his hat not being found upon his head, but at some distance from him, it did not appear, against what part of the head that hole was made.
Upon the rest of his Cloaths, I do not know of any further effect, nor did we smell any sulphurous scent about them: which might be, Partly because it was now a good while after the time, and Partly by reason of their being presently drenched in the water into which he fell.
The night following, the three Doctors above mentioned, and my self, with some Chirurgions (besides a multitude of others) were present at the opening of the head, to see if any thing could be there discover'd; but there appear'd no sign of contusion; the brain full and in good order; the nerves whole and found, the vessels of the brain pretty full of Blood. But nothing was by any of them discern'd to be at all amiss. But it was by candle-light, and they had not time to make very nice Observations of it (the Body being to be buried by and by) and the croud of People was a further hindrance. But if any thing had been considerably out of order to the view, it would surely have been by some of them discover'd. Some of them thought, they discern'd a small fissure or crack in the skull; and some who held it, while it was sawing off, said, they felt it Jarring in their hands, and there seem'd to the eye something like it, but it was so small, as that by candle-light we could not agree it certainly so to be.
Some of the Hair on the right Temple was manifestly singed, or burnt; and the lower part of that Ear blacker, than the parts about it, but soft; and it might be only the settling of the Blood. The upper part of the left shoulder, and that side of the neck, were also somewhat blacker than the rest of the Body, but whether it were by the blow, which broke the collar, and scorch'd the round red spot thereupon, or only by settling of the Blood, I cannot say; yet I think, it might very well be, that both on the head, and on this side of the neck, there might be a very great blow, and a contusion upon it (and seems to have been so, by the tearing of the hat, and breaking the collar, if not also cracking of the skull) and yet no sign of such contusion, because dying so immediately, there was not time for the Blood to gather to the part and stagnate there (which in bruises is the cause of blackness) and it was but as if such a blow had been given on a Body newly dead; which does not use to cause such a symptom of a bruise, after the Blood ceases to circulate.
Having done with the Head, they open'd the Breast, and found that burning to reach quite through the skin, which was in those scorch'd places hard and horney, and shrunk up, so as it was not so thick as the soft skin about it: but no appearance of any thing deeper than the skin; the Muscles not at all disorder'd or discolour'd (perhaps, upon the reason, that was but now said of the Head, Neck and Shoulder). Having then taken of the Sternum, the Lungs and Heart appear'd all well, and well-colour'd without any disorder.
This is the sum of what was observ'd; only that the whole Body was, by night, very much swell'd, more than in the morning; and smelt very strong and offensively: Which might be by the hotness of the weather, and by the heat of the place occasion'd by the multitude of People.
An Experiment, To examine, what Figure, and Celerity of Motion begetteth, or encreaseth Light and Flame.
This was communicated by. Dr. Beale, as follows;
May 5. 1665. fresh Mackrels were boyl'd in Water, with salt and sweet herbs; and, when the Water was perfectly cold, the next morning, the Mackrels were left in the Water for pickle.
May 6. more fresh Mackrels were boyl'd in like Water; and May 7. both Water and Mackrels were put into the former Water, together with the former Mackrels. (Which circumstances I do particularize, because, whether, the mixture of the pickle of several ages, and a certain space of time, or whatever else was necessary, and wanting, the trial did not succeed with like effect at other times).
But now on the next Munday (May 8); evening, the Cook stirring the Water, to take out some of the Mackrels, found the Water at the first motion. become very luminous, and the Fish shining through the Water, as adding much to the Light, which the water yielded; The water By the mixture of Salt and Herbs, in the boyling, was of it self thick and rather blackish, than of an other clear colour: yet being stirr'd, it shin'd, and all the Fish appear'd, more brightly luminous in their own shapes.
Wherever the drops of this water (after it was stirr'd) fell on the Ground, or Benches, they shin'd: And the Children took drops in their hands, as broad as a penny, running with them about the house, and each drop, both near and at distance, seem'd by their shining as broad as a six pence, or a shilling, or broader.
The Cook turn'd up the side of the Fish, which was lowest, and thence came no shining: and after the water was for some good time settled, and fully at rest, it did not shine at all.
On Tuesday night (May 9). we repeated the same Trial, and found the same effects. The water, till it was stirr'd, gave no light, but was thick and dark, as we saw by day-light, and by candle-light. As soon as the Cook's hand was thrust into the water, it began to have a glimmering; but being gently stirr'd by the hand moving round (as the Dairy-maid do to gather the Curds for Cheese) it did so shine, that they, who look'd on it at some distance, from the further end of another room, thought verily, it was the shining of the Moon through a Window upon a Vessel of Milk; and by brisker Circulation it seem'd to flame.
The Fish did then shine as well from the Inside, as the Outside, and chiefly from the Throat, and such places, as seem'd a little broken in the boyling.
I took a piece that shin'd most, and fitted it as well as I could devise in the night, both to my great Microscope, and afterwards to nay little one; but I could discern no light by any of these Glasses; nor from any any drops of the shining water, when put into the Glasses. And May 10. in the brightest rayes of the Sun, I examin'd, in my great Microscope, a small broken piece of the Fish, which shin'd most the night before. We could find nothing on the surface of the Fish very remarkable. It seem'd whitish, and in a manner dried, with deep inequalities. And others, as well as my self, thought, we saw a stream, rather darkish, than luminous, arising like a very small dust from the Fish: And rarely here and there, a very small; and almost imperceptible sparkle in the Fish. Yet of these sparkles we are certain; we numbred them, and agreed in the number, order and place. Of the steam I am not confident, but do suspect our Eyes in the bright Sun, or that it might be some dust in the Aire.
The great Microscope being fitted in the day-light for this piece of Fish, we examin'd it that night, and it yielded no light at all, either by the view of the Glass, or otherwise.
Finding it dry, I thought that the moisture of Spittle, and touching of it, might cause it to shine: and so it did, though but a very little, in a few small sparks, which soon extinguish'd. This we saw with the bare eye; not in the Glass.
The Fish were not yet fetide, nor insipid to the belt discerning palats: And I caused two Fish to be kept for further Tryal, two or three days longer, till they were fetide in very hot weather; and then I expected more brightness, but could find none, either in the water, by stirting it, or in the Fish, taken out of the water.
And some Trials I made afterwards with other boyl'd Mackrels (as is above said) with like pickle, but fail'd of the like success.
This season serves for many Trials in this kind, and by bet-bet Microscope, or better ordered. And in these Vulgarities we may perhaps as well trace out the cause and nature of Light, as in jewels of greatest value, &c.
Some Considerations Touching a Letter in the journal des Scavans of May 24. 1666.
In Num. 9. of these Transactions were publish'd the Schemes and Description of certain Ways of Sounding the Depth of the Sea without a Line; and of Fetching up Water from the bottom of it; together with some Experiments already made with the former of these two Contrivances. The Author of the French Journal des Scavans found good, to insert them both in his Journal of May 3. but in another of May 24. intimates, that the said Schemes and their Descriptions are not very clear and intelligible (he means, that they were not well understood by French Readers) proposing also some Difficulties, relating to that Subject, and esteemed by him necessary to be satisfied, before any use could be made of the said Instruments.
Upon this occasion, the Author of these Tracts thinks fit, here
First, That Englishmen and such others, as are well versed in the English tongue, find no difficulty in understanding the descriptions of these Engines, nor in apprehending their structure, exhibited by the Figures, especially if notice. be, taken of the Emendation, expelled at the end of Num. 10. about the misgraving the Bended end of the Springing Wire (which it seems has not been noted in France, tho' the said Num. 10 is known to have been seen there a pretty while before their Journal of May May 24. was publish'd). And as for the particular of the Bucket, fetching water from the bottom of the Sea, both the figure and the annexed Description thereof are so plain. and clear, that tis some wonder here, that any difficulty, of understanding them is pretended by any, that hath but ordinary skill in Cutts: and the English language. Mean while, that way, which the French Author that recommends for this purpose as more simple, Videl. a Brass-Pump with double Valves, is not at all unknown in England, nor his bin left untried there; but was found inconvenient, in respect that the Valves in descending did not fully open, and give the water a free passage through the Cavity of the Vessel, nor in ascending shut so close, as to hinder the water from coming in at the top: Whereas by the way proposed in Num. 9. both is perfom'd with great ease and security.
Secondly Whereas the French Author is of opinion, that 'tis unknown, how, much time a Heavy Body requires to sink in water, according to a certain depth; he may please to take notice, that that hath been made out in England by frequent Experiments; by which, several Depths, found by this Method of founding without a Line, were examin'd by trying them over again in the same place with a Line, after the common way. And as to that, Quære of his, Whether a heavy Body descends in the same Proportion of swiftness in Witter, that it would do in Air?
The Answer is, that it does not; but that, after it is sunk one or two fathoms into the Water, it has there arrived to its greatest swiftness, and keeps, after that, an equal degree of velocity; the Resistance of the water being then found equal to the Endeavour of the heavy Body downwards.
Thirdly, When the same Author alledges that it must be known, when a Light Body reascends from the bottom of the water to the top, in what proportion of time and swiftness it rises. He seems not to have considered, that in this Experiment, the times of the descent and ascent are both taken and computed together; so that for this, purpose, there needs not that nicety, he discourses of.
Fourthly, Whereas it is further excepted, That this way of Sounding Depths is no new Invention; The answer is ready, that neither is it pretended to be so, in the often quoted Tract; it being only intimated there, that the manner of performing it, as it is in that place represented and described, is new.
Lastly, To rectifie the said Author's mistake, as if the instrument of fetching up Water from the bottom of the Sea, were chiefly contriv'd, to find out, Whether in some places of the Sea any Sweet Water is to be met with at the bottom: There will need no more, than to direct him to the Book it self Num. 9. where p. 149. towards the end, the First use of this Bucket is express'd to be, to know the degrees of saltness of the Water according to its nearness to the top or bottom; or rather to know the constitution of the Sea-water in several depths of several Climates, which is a matter, much better to be found out by Trial, than Discourse. Neither is it any where argued in that Book (as the French Journal insinuates) that, because sweet water is found at the Bottom of the Sea of Baharem, therefore it must, but only that it may, be found so elsewhere. And since the same Journal admits, that those Sweet water-springs, which yield the sweet water, that is found at the said place, have been formerly on the Continent, far enough from the Sea, which hath afterwards covered them. It will be, it is presumed, lawful to ask, Why in many other places there may not be found the like? And besides, how we do know, but that there may be in other parts, Eruptions of large Springs at the bottom of the Sea, as well as there?