Popular Science Monthly/Volume 84/February 1914/The Physical Laboratory and its Contributions to Civilization
|THE PHYSICAL LABORATORY AND ITS CONTRIBUTIONS TO CIVILIZATION|
ALTHOUGH physics is one of the oldest and most respectable of the sciences, it must be acknowledged with regret that many otherwise well-educated persons have but a vague idea of its scope, and the question, "What is a physical laboratory and what does one do in it?" is by no means a rare one. The science of physics or natural philosophy, as it was called by Newton, properly includes the study of all natural phenomena that are not concerned with life, as distinguished from biology, which undertakes to investigate the phenomena of living organisms. To speak more particularly, physics deals with mechanics or the phenomena of motion and its causes, including those motions which we characterize as sound; with heat, light, electricity and magnetism and those new phenomena which have to do with radio-activity and the recently discovered new sorts of radiation. It is thus impossible to make any classification of physics which shall exclude astronomy, which is divided into celestial mechanics or the study of the motions of the sun, planets, comets and stars, and the new science of astrophysics, or the study of the physical and chemical constitution of the stars mainly by means of the spectroscope invented only about fifty years ago, or which shall exclude chemistry, which now more than ever before is concerning itself with the relations of different elements and their compounds to phenomena of heat, electricity and light. Geology has mainly to do with the applications of physics to the surface of the earth. Nevertheless, for purposes of convenience it has become customary to divide off these other sciences from physics proper and to have them studied and taught by separate professors.
If we examine the history of physics we shall find that this division came very late, perhaps not much more than one hundred years ago. The first physical phenomena to be studied were, undoubtedly, those of day and night, the rising and setting of the sun and moon, and the changes of the seasons. We know very well that a people as highly cultivated as the Greeks, although they were deeply interested in natural phenomena, had an extremely small knowledge of the laws of nature and had not learned how to investigate them. Although they possessed an excellent knowledge of geometry, they had not the slightest idea of the nature or laws of motion, whether celestial or terrestrial, and with the exception of the properties of the lever and of liquids at rest, known to Archimedes, their knowledge of physics was almost a blank, and yet their great philosopher, Aristotle, dominated science until the sixteenth century of our era. It was at this time that the dawn of modern physics took place with the beginning of the experimental study of nature by Galileo. We must remember that Aristotle suffered not so much from lack of knowledge as from lack of appliances. What might he not have discovered had he possessed a thermometer, a telescope or even a clock! Nevertheless, Galileo did not possess these simple instruments, but he went to work to make them possible. He invented the telescope and thus made possible the searching of the mysteries of the heavens. Although he had no clock, he studied the motions of the pendulum, formed by the great lamp in the baptistery at Pisa, by comparing the time of its swing with the number of beats of his pulse, thus making possible the application of the pendulum to clocks by Huygens. As a contrast of Galileo's method with that of the Greeks may be cited his experiment of dropping a light and a heavy body from the top of the leaning tower of Pisa and showing that both fell to the ground at the same time, instead of believing, as the Greeks had done from reasoning without experiment, that the heavy body falls the faster. By careful study of the motions of a ball rolling down an inclined plane, Galileo was able to enunciate the precise law of falling bodies; that their acceleration is uniform, that is, that in equal times their velocity increases by equal amounts. The way was thus prepared for Newton, who in the next century established the connection of all forces with the accelerations produced by them and was able to enunciate the laws of motion, both terrestrial and celestial, in a form that has not been improved upon to-day, constituting one of the most magnificent triumphs of the human intellect. Passing on rapidly we find at the beginning of the nineteenth century the phenomena of electricity beginning to attract the attention of investigators, while those relating to light had already made substantial progress. All this time there had been nothing that could properly be called a physical laboratory. Discoveries had been made by individual inquirers working generally in such rooms as they had in their own houses with the most meager facilities. We all remember how Newton bored a hole in the wooden shutter of his window in order to admit a narrow beam of light which was to be dispersed into a spectrum by his prism. Even as late as the middle of the nineteenth century the celebrated determination of the velocity of light was made by Foucault, who is said to have been so poor that he was obliged to hire a pair of telescopes at an optician's and to make the experiment in his own rooms. In fact, physical research had reached a very great extension before the provision of special buildings in which to carry it on had been thought of, and these were first provided in connection with instruction. It was not until 1874 that the celebrated Cavendish laboratory was completed at the University of Cambridge, and it is worth remarking that this great laboratory, out of which has proceeded a large number of the most remarkable modern discoveries in physics, was built at a cost of little over $40,000. It is interesting to know that the introduction of laboratory studies at Cambridge was attended with much shaking of heads and it seemed necessary to Maxwell, the first professor of experimental physics there, to justify its introduction in his opening lecture. "But what," he says, "will be the effect on the university, if men pursuing that course of reading which has produced so many distinguished wranglers turn aside to work experiments? Will not their attendance at the laboratory count not merely as time withdrawn from their more legitimate studies, but as the introduction of a disturbing element, tainting their mathematical conceptions with material imagery and sapping their faith in the formulas of the text-books?" A more amusing doubt was that expressed by Todhunter, himself a distinguished mathematician and student of natural phenomena. "What is the use," said he, "of a student's confirming a physical phenomenon by an observation in the laboratory? If he will not believe the statement of his tutor, who is presumably a gentleman of exemplary character in holy orders, what use can there be in his repeating the experiment for himself?" It is needless to say that this point of view has long since passed into oblivion and the strong point of the laboratory is that it enables the student to himself verify the laws of nature quite independently of the statements of any authority whatever, however respectable.
The purposes of our laboratories then are twofold. First, in them we teach our students the use and manipulation of instruments and the methods for the precise verification of physical laws. In this way the student becomes accustomed to habits of accuracy and the reporting of what he actually sees without the aid of the varnish of imagination and unaffected by any prejudices as to what result he expected to get. We thus have an education in morals which is hard to equal in any other part of education. As a simple example let us consider the method in which the student studies the motion of the pendulum in the elementary laboratory. Instead of measuring the time of its swing by his pulse beats in the manner of Galileo, he compares it with the beats of an accurate astronomical clock, which he perceives by his ear while with his eye he notes the passage of the wire which supports the ball of the pendulum across an accurate mark, thus being obliged to use the senses of sight and hearing at the same time. He must then measure the length of the wire accurately as well as the diameter of the ball which hangs from it. Later on, as there will be difficulty in telling where the string or wire ends, more refined means must be adopted for defining and measuring its length. From the results of these measurements the student will by means of theory be able to calculate the result expressing the intensity of gravity and as he presumably knows the correct value, he will be under a certain temptation to so "doctor" his results as to make his work seem accurate. It is needless to say that such doctoring can never be tolerated and is totally incompatible with the character of a true scientist. The example which I have given shows the nature of almost all the work that is undertaken in the physical laboratory. In every experiment certain data are taken which enable us to give a numerical measure of the properties of certain bodies, or a statement of the numerical relations involved in phenomena. As an example we may take the question of the determination of the specific heat of bodies, that is to say, of the amount of heat required to heat a body through a certain range of temperature. For this purpose the body, say an iron ball, is heated to a certain definite temperature, let us say by being immersed in the steam of a boiler in which water is boiling. The ball is then dropped into a vessel containing a known quantity of water and the heat that it gives out in cooling is measured by the rise in temperature which the water undergoes. This apparently simple process is found to be attended with a great deal of difficulty. In the first place, the determination of the temperature of the ball, when in the steam boiler, is no easy matter. A thermometer immersed in the steam as near the ball as possible may not show exactly the temperature of the ball. Secondly, if the stem of the thermometer is entirely immersed in the hot steam the temperature shown would be different from that when only, the bulb of the thermometer is in the hot steam and the stem in the cool air. Thirdly, it will be difficult to transfer the ball from the hot steam to the cold water so quickly that it will not have lost some of its heat, which we want to measure, before it gets into the water. Fourthly, as soon as the temperature of the water in the calorimeter, as it is called, begins to rise the calorimeter begins to lose heat by radiation to outside bodies. In order to estimate this we must first study the laws of such radiation by allowing water previously heated to cool in the calorimeter and observe how rapidly its temperature falls. Finally, it is necessary to know accurately how much water was in the calorimeter, which is found by weighing, but during the whole experiment water is being lost by evaporation. When we consider all these corrections that must be carefully made as well as the fact that to accurately read the height of the mercury in the thermometer it would probably be necessary to look at it with a telescope, the difficulties in this simple experiment and the temptation to slight something are very apparent, and yet this is what we expect a freshman to do in the time of about two hours in the laboratory, and at the same time we expect his result to have an accuracy considerably better than one part in a hundred.
The second and in many cases far more important function of the laboratory is to serve as a place for the performance of accurate research, that is, the investigation and discovery of new phenomena. In order to take part in this inspiring occupation it is obvious that the student must have acquired a considerable amount of proficiency and have already made measurements of a great variety involving a high degree of precision. It is often supposed that scientific discoveries are attended with a large amount of luck, or that they are the result of a sudden inspiration which may come to anybody. Such is far from being the case. Professors of physics are frequently the recipients of visits from persons who in their enthusiasm feel that they have made an important discovery, which in many cases has been thrown off as a sort of by-product in some other vocation. Not many years ago I received a visit from a young man who had traveled over two hundred miles to present to me the results of a theory which he had elaborated to account for the motion of rotation of the planets on their axes. After I had inquired whether he had made himself familiar with the writings of the great masters in celestial mechanics, and had explained to him the impossibility of his theory, I asked him this question, "Do you realize, my dear sir, that if your theory were correct, it would upset the consequences of all the astronomical observations that have been made during the last two hundred years?" The young man went away sadder but wiser and I did not hear from him again. As a matter of fact discoveries are seldom made by persons not possessing the training that I have described, and in ninety-nine cases out of a hundred the element of chance is reduced to the smallest possible dimensions.
I have already stated that the provision of great physical laboratories in connection with instruction is extremely modern. In England the pioneer work in systematized instruction was done in Oxford and London about 1867. The Clarendon Laboratory at Oxford was built from 1868 to 1872, while the Cavendish Laboratory in Cambridge was, as has been stated, not opened until 1874. In this country the first systematic laboratory course in physics was organized about 1870 by Professor E. C. Pickering, at the Massachusetts Institute of Technology, which illustrates one of my points that I have already made, for Professor Pickering has now been for about thirty-seven years the head of the astronomical observatory at Harvard. The present physical laboratory at Harvard was built in 1884. Of late years laboratories have been built at all our colleges, and there has developed a tendency to make them very large and costly. Two of the latest, the Palmer Laboratory at Princeton and the Sloane Laboratory at Yale, have gone well beyond the quarter of a million mark. The largest and best equipped laboratory in the country is that belonging to the national government, and known as the Bureau of Standards, which, in its brief history of about ten years, has had over two millions of dollars spent upon it. When we consider that this institution is entirely separated from teaching, we must believe that work of great importance is done there to justify this great outlay. Permit me to describe what some of the functions of such a laboratory are, and incidentally to explain some of these devices that are to be found in any great modern laboratory.
At the Bureau of Standards we find five large buildings, each devoted to a particular purpose. These have cost $712,000. In the largest we find the divisions of weights and measures, of heat, and of light. The chief objects of the Bureau of Standards being necessarily practical, the researches undertaken there are limited in scope by this consideration. Nothing is perhaps more practical than the verification of the standards of weight by which commodities are bought and sold. Even the weights of the mint are tested at the Bureau of Standards. Accordingly in a basement room mounted upon heavy brick piers, which are a prominent feature in every physical laboratory in order to secure freedom from vibration, we find extremely accurate balances, some of which are capable of weighing a body with an accuracy of one part in fifteen or twenty millions. The comparison of two equal weights is probably susceptible of greater accuracy than any other physical operation. It is to be remarked that in order to attain this degree of accuracy the balance has to be operated in vacuo, the whole instrument being placed in a case from which the air is pumped out, and all operations of transferring the weights being conducted from a distance by means of controlling rods or shafts, since the heat of the observer's body near the balance would so change the length of the beam as to render such an accuracy impossible.
Next to weighing comes the measurement of length, which is susceptible of about the same accuracy. Here again, the effect of changes of temperature in causing metal scales to expand has to be provided against, so that the work has to be carried on in a subterranean vault, where the changes of temperature are made as small as possible. In the division of heat great practical importance belongs to the measurement of temperatures. Thousands of thermometers of all sorts are sent here yearly to be tested. Before the existence of the Bureau of Standards there was no official means of verifying the accuracy of clinical thermometers used by every physician in diagnosing disease. Here these thermometers are placed, perhaps a hundred at a time, in a bath of water whose temperature is controlled, by thorough stirring, to an equality of temperature of less than a hundredth of a degree. Of great importance is also development of a means of measuring high temperatures, such as those of red or white heat, at which glass would melt. For these high temperatures it is necessary to use a thermometer-bulb of platinum or some more infusible metal, and filled, instead of with mercury, with some gas. For practical purposes, such as the determination of the temperature of furnaces for porcelain, or for the treatment of steel or the annealing of glass, the temperature may be measured by the comparison of the color of the light emitted by the substances in question with that of a filament heated by a known electric current.
In the division of light one of the most important practical matters is the measurement of the intensity of sources of light, particularly of incandescent electric lights, for when one pays a certain amount he desires to get the largest amount of light possible for his expenditure. It is of interest to know that the amount of light obtained for a certain amount of electrical energy has been increased at least ten times in the last few years by the introduction of the filament of the metal tungsten instead of carbon. Another matter of practical importance in the division of light is the determination of the action of quartz crystal and other substances in twisting the so-called plane of polarization of light, since by this property the strength of sugar solutions is measured, and by such tests the rate of duty is fixed that sugar shall pay.
Two large buildings are devoted to electrical and magnetic research. The enormous development of the production of electricity, whether for light, power or transportation purposes, has rendered the exact specification of its standards of measurement of superlative importance. For over forty years such researches have been carried on in many countries, with ever-increasing precision, but still with certain small discrepancies between the determinations of different national laboratories. For instance, the unit of electric current is practically defined by the weight of silver that it will deposit from a solution in a given time. Owing to the discrepancies in the values obtained, the happy idea occurred to Dr. Stratton, the director of the Bureau of Standards, of inviting the national laboratories of England, France and Germany to send each a delegate to the Bureau of Standards in Washington, where each would carry on measurements by his own methods on the same current traversing all the instruments, thus the discrepancies were much reduced and physics was made to contribute to international good feeling. Besides these researches to establish the standards, which we have already seen to be necessary in heat, light and electricity, many tests are required on the properties of materials, such as the magnetic properties of iron that is to be used in dynamo-electric machines. All engineering is but applied physics, and a whole building has been devoted to the testing of materials used in engineering and in manufacturing, such as the strength of steel and iron, of concrete, and other materials used in construction, of thread, paper, leather and textile manufactures. It is known that the government buys all its supplies on specification, and for many of the bureaus the testing is carried on at the Bureau of Standards. In addition the Bureau has two branches, one at Pittsburgh, for testing structural materials, and one at Northampton, Pa., for testing cement, where all the cement used in the Panama Canal is tested. It is easy to see how under this rigid testing many improvements of importance to manufacturers are developed, and in this way industry is largely promoted. In fact the bureau is now of as much interest to manufacturers and engineers as it is to physicists.
I have now said enough to show the direct practical importance to the country of a laboratory in which testing, as well as research, is done, even though no teaching is done there. But when I speak of contributions to civilization I do not by any means limit myself to the increase of human comfort, and to the increasing of the production of wealth. Neither do I consider this as the main object of science, nor its chief justification, although it is one that is most easily apprehended by all intellects. Science does not consist in the observation and classification of facts that are useful in this narrow sense, but rather in the fitting of them into a great and harmonious system, that convinces us of the reasonable scheme of nature, and gives us the same esthetic pleasure that the performance of a great piece of music affords, and lifts our spirits to the contemplation of the author of that great scheme of nature, of which, however much we learn, an infinitely greater amount remains for us still to explore. It is only to those who have personally wrestled with nature in the attempt to make her yield up her secrets that this highest aspect of science is revealed. Fortunate are those who, untrammeled by practical ends or the hope of gain, can devote their lives to the calm, undisturbed questioning of nature, and such should our college professors be. It is not yet generally understood that professors should be paid such salaries that they may take this high view of their calling, without being disturbed and in a large degree prevented from fulfilling these highest duties by the struggle for existence.
I shall now, having described some of the objects and means of research in physical laboratories, attempt briefly to trace the history of one or two notable discoveries of the last quarter of a century, with the results of which at least the public is in a large measure concerned. One hundred years before the present time, almost all that was known of electricity was embraced in the knowledge obtained by the Frenchman Coulomb regarding the law of force with which electricity at rest upon conducting bodies attracts and repels other electricity. Nothing was known of the phenomena of electricity in motion, flowing, as we say, in a current. It was not until 1827 that the law stating the dependence of the strength of the current on the driving-power of the battery causing it was discovered by the German Ohm. But a fundamental discovery was made in 1820 by the Dane Oersted when he found that the current in a wire would act upon a magnet anywhere in its vicinity, or would produce what we now call a magnetic field. Upon this discovery depends the possibility of all our telegraphs, for which the current was soon utilized. But a more powerful intellect than that of Oersted, namely that of the Frenchman Ampère, inspired by Oersted's discovery that a current acted like a magnet, reasoned that in that case two currents would exert magnetic forces upon each other, and in a wonderful series of researches determined the mathematical laws of these mutual actions of currents in the most complete manner. When we see the primitive apparatus with which Ampère made these brilliant discoveries, we are led to have the most profound admiration for his brilliant experimental and mathematical genius, and we may secretly wonder whether we have not laid too much emphasis to-day on fine laboratories and equipments. The next commanding genius that appears on the scene, whose work is more important than any of those yet mentioned, is Michael Faraday, professor at the Royal Institution, a laboratory for research and popular lectures, founded by our own countryman who later became Count Rumford, but made forever famous by the discoveries there made during a long term of years by Faraday. Those who have visited the laboratories at the Royal Institution will be surprised at the total lack at that time of all the conveniences that we today expect, but Faraday was no doubt perfectly satisfied with it. Today electric lighting and supply of current in a laboratory is a commonplace—then there was not even gas, and all currents had to be made by batteries laboriously filled with chemicals for each time of use. There was no insulated wire, and Faraday had to wind his own with thread or ribbon. Among the greatest triumphs of Faraday was his discovery of the converse of the production of magnetism by electrical current; I mean the production of current by magnetism. After long attempts, he found that if a magnet was moved into, out of, or in the neighborhood of a coil of wire forming a complete circuit, then a current of electricity was induced, as he put it, in the coil during the motion of the magnet. This is the germ of our dynamo-electric machines which to-day supply all the current for our light, power and electric traction. Could Faraday have seen the huge dynamos of ten thousand horsepower each that convey the power of Niagara Falls to regions a hundred miles away, he might feel the enormous importance of the work that he had accomplished to the world at large, but I much doubt whether he would have felt a more lively satisfaction than when he first saw the electric spark jump between the ends of his coil surrounding the magnet. The chief question which interested Faraday during the greater part of his life was the question of action at a distance. How can the motion of a magnet or what amounts to the same thing, the change of current in one coil, cause a current to flow in another coil in a different place. This he explained by some change in the medium surrounding the coils, but it was reserved for another to give the complete explanation. This was Clerk-Maxwell, of whom I spoke at the beginning, who was the chief expounder of Faraday's views, to which he added and which he made precise by his wonderful ability to put them into mathematical form. It was Maxwell's brilliant idea that the medium which is affected by the presence of an electric current is nothing else than the ether which is supposed to convey the waves of light, and it was a result of his theory that the electric and magnetic actions are transmitted through the ether in the form of waves. Not only this, but he showed that the velocity of these electromagnetic waves would be exactly that of light. He then made the startling generalization that light waves possess all the characteristics of electromagnetic waves, and in fact differ from them in no essential way. These ideas of Maxwell, first put forward nearly fifty years ago, have now found universal acceptance, and the whole world believes that light is an electromagnetic phenomenon. But it was a long time before Maxwell's ideas were accepted, especially on the continent of Europe. For Maxwell died in 1879 without ever having demonstrated experimentally that electric and magnetic effects are propagated in waves. This was reserved for another, the German Heinrich Hertz, who in 1887-88 was able to demonstrate the propagation of such effects with a definite velocity, which was found to be indeed the same as that of light.
Hertz's first experiment by which this discovery was made was so simple that it may be described. If we have two metal spheres near enough together a spark will pass between them if they are electrified, but only if the electrical potential or pressure is different for the two balls. If the two balls form the ends of a circuit of wire, the whole may be electrified as strongly as we please with never a sign of a spark passing between the balls, for the whole conductor has the same potential. But Hertz found that if the wire, in the form of a rectangular circuit, was connected with one of the ends of an induction coil producing sparks, each time that a spark passed from the induction coil a spark also passed between the balls of the rectangle. This was always supposing that the connection was made to a point of the rectangle not symmetrically placed with respect to the balls, and Hertz explained the phenomenon by supposing that the current flowed in both directions in the form of a wave, taking longer to go to one ball than to the other, so that there would be a difference of potential between the balls, and hence the spark. This was corroborated by the fact that when the connection to the induction coil was at a point symmetrical to the two balls, there was no spark, for then the wave arrived at both balls simultaneously. This experiment was the first to show the propagation of electric current in the form of waves, and Hertz calculated the time of such a wave running back and forth in the wire as the one-hundred-millionth of a second. The possibility of making such rapid oscillations opened up a whole new field of research, which has been greatly exploited in the last twenty-five years. Not only did Hertz show that the current in a wire was propagated in waves, but he also showed that the electromagnetic effects which are able to induce currents in other wires are also propagated across free space in waves. These waves traverse various obstacles, and are stopped only by conducting bodies. Many persons undoubtedly had the idea that these waves traveling through space might be used for signalling purposes, but it was due to the patience and pertinacity of Guglielmo Marconi that these waves, sent by Hertz a distance of a few score feet, might travel across the Atlantic Ocean and still retain the power of exciting a current in a wire properly set up to receive them. It was only in 1895 that Marconi first began his experiments on electric waves, and in the short time of seventeen years wireless telegraphy has become so important to commerce, not only in connection with the reception of intelligence from ships in distress, but for overland communication in certain remote regions of the earth that last summer a conference was held in London where representatives of over forty nations met to negotiate a treaty for the regulation of wireless communications at sea. I had the honor of being a delegate of the United States government to this conference, and during the five weeks of our proceedings, noting the caliber of the delegates sent by the different governments and the seriousness with which every detail was threshed out in the most diplomatic language, I became vividly impressed with the importance of wireless telegraphy to civilization, and again I thought of the work of Faraday in 1830, Maxwell in 1864, Hertz in 1887, as crowned with a success that they could never have foreseen.
Leaving the domain of electrical waves let us turn to another sensational discovery of seventeen years ago. We have seen that wireless telegraphy had been prepared for by the work of nearly three quarters of a century. In December, 1895, the world was startled by the announcement that Professor Röntgen, of Würzburg, had obtained from vacuum tubes in which an electric discharge was passing a new sort of rays, which, though invisible, would yet affect a photographic plate and also possessed the startling power of being able to pass through many opaque substances, while casting shadows of others. Most wonderful seemed the statement that by these rays the bones of the hand could be seen. Seventeen years later these Röntgen rays are used in every hospital, and reveal the inmost secrets of the body. But this is not their interest to the physicist, but rather the fact that they have opened up a whole field of facts previously unsuspected, so that an investigator ignoring them would to-day be held the greatest of old fogies. How did Röntgen come to discover the X-rays? No doubt there was a certain element of chance. We are told that he had covered the discharge tube, the so-called Crookes tube, with black paper, so that no light should get out from it, and that Röntgen's attention was attracted by the fluorescence, or faint shining with light, of a piece of paper lying on the table, the paper being covered with the salt of barium platinocyanide. But why did this piece of paper coated with this uncommon chemical happen to be lying on the table, and why had Röntgen covered the Crookes tube with black paper? We find that barium platinocyanide was one of the substances that had been investigated by previous investigators as to its fluorescence, and that such paper was a commercial article in Germany. Röntgen must then have suspected that there was some property of the Crookes' tube that would cause fluorescence, so that the presence of this fluorescent paper was not accidental at all. This is then a striking example of what I have before stated. A further one is given by a discovery made the next year in Paris. Röntgen's discovery had set the world on fire, and had given rise to a renewed interest in the subject of fluorescence. Noteworthy among fluorescent substances are the salts of uranium, and these were examined by Henri Becquerel, the third generation of physicists of that name. Becquerel placed uranium salts against a photographic plate wrapped up in black paper, and soon found that the plate was affected, even through the opaque paper. At first Becquerel thought that the uranium had this property only after being exposed to the sun's light, but he soon found that the same properties were possessed by uranium salts that had been formed in the dark, and had never seen the sun. In short these salts are constantly emitting a new sort of radiation, now known as Becquerel rays. Physicists now began to look for other substances than uranium which had these properties, with the result that it was found that uranium-bearing ores were found to contain other substances having the properties in a far higher degree, and at last the Curies were able to separate a new element, which was named radium. The field of radioactivity thus opened up has become an enormous one, and many substances have been discovered having radioactive properties. Here is again an illustration of the impossibility of distinguishing between physics and chemistry, for although Mme. Curie is a chemist, the Nobel prize in chemistry was awarded a few years ago to Professor Rutherford, professor of physics at the University of Manchester, England. Time will not permit me to go on with the history of this fascinating subject, but I will only remark that in all the great countries radiological institutes have been founded for the purpose of carrying on researches on the medical applications alone of radioactivity, so that here again we may expect great practical results.
I hope I have now sufficiently shown the nature of the contributions of the physical laboratory to civilization, not only in the practical matters of making life easier and more agreeable, but also in the extension of our intellectual outlook, and the making of life more worth living.