are for some reason or other continually projecting at enormously great velocities. two kinds of particles, one will not be surprised to find that these substances maintain a temperature above that of the surrounding atmosphere. This has been proved experimentally only for radium, which has been found by MM. Curie and Laborde to remain permanently at a temperature between one and two degrees centigrade above that of its surroundings, and to give out for each gram.of its weight enough heat per hour

FIG. 4. RADIOGRAPH OF KEYS.

From a plate taken by means of radium, by W. P. Near, B. A., assistant to Prof. J. C. McLennan, in the Physical Laboratory of the University of Toronto. In the taking of the radiograph of which the above is a reproduction, the keys were placed upon a sensitized photographic plate protected by cardboard. Time of exposure, 40 minutes, Strength or intensity of radium, 1,500,000. The reader will note the resemblance of the result to that obtained by means of X-rays.

to raise a hundred grams of water through one degree. Since radium radiates over a million times more actively than either of the other substances, it is not probable that any one will ever be able to show directly by experiment that uranium and thorium also maintain temperatures above that of their surroundings. Nevertheless, in all probability, the same causes that operate to maintain the relatively high temperature of radium operate also to keep up the temperature of both of the other radioactive substances, the only difference being one of degree. Hence it is probable that all radio-active substances are constantly emitting heat energy to a greater or less degree. This is not sur

such substances are constantly sending forth from their surfaces streams of particles propelled with almost incredible velocity; for if these particles are projected from all of the molecules of the active substances, it would, as a natural result, be expected that the temperature of the substance would rise under the unceasing internal bombardment.

But from what source comes this energy represented in the projected particles, and of which this heat and light are the ultimate manifestation?

Radio-activity a Manifestation of Subatomic Energy

The answer to this last question has not yet been fully given. This much, however, can be said thanks to the magnificent work of Rutherford of McGill University, of Sir William Crookes in England, of the Curies and of Becquerel in Paris, and of one or two German physicists-that a fairly satisfactory answer is at least in sight.

Whatever be the cause of the ceaseless emission of particles by radio-active substances, it is certain that it does not lie in any ordinary chemical reactions such as those with which we have heretofore been familiar; for Madame Curie proved, when she originally discovered the activity of thorium, that the radial energy of all the active substances is proportional simply to the amount of the active element (uranium, thorium, or radium) which is present, and has nothing whatever to do with the nature of the chemical compound in which that element is found. Another most striking property of radio-activity is that it is independent of all changes in physical as well as chemical conditions. A radioactive substance can be subjected to both the lowest and the highest temperatures obtainable without showing any alteration whatever in the degree of its activity. Radio-activity seems therefore to be as unalterable a property of the substances possessing it as does weight itself. It is therefore something entirely beyond the range of ordinary molecular forces. This is certainly strong evidence in favor of the view that radio-action involves a change in the nature of the

The present is the first time in the history of science that any subatomic store of energy has been tapped by man.

The Mechanism of Radio-activity

It seems probable from the discoveries described above, together with other dis

FIG. 5. RADIOGRAPH OF MEDAL AND COINS.

Taken by means of radium, in the Physical Laboratory of the University of Toronto. In this case, as in that of Fig. 4, the sensitized plate, with the metallic objects upon it, was protected from direct action of the radium rays by means of a cardboard screen. Time of exposure, 50 minutes. Intensity of radium, 1,500,000.

coveries which cannot here be recorded, that the atoms of radio-active elements are undergoing a slow but continuous process of disintegration into atoms of smaller mass and simpler form. Just why these atoms are disintegrating, and just how these new types of matter are formed, must as yet, of course, be largely a matter of speculation; nevertheless research has gone far enough to enable us to form a reasonably plausible hypothesis as to the mechanism of radioactive change.

In presenting this hypothesis, the first remarkable fact to be noted is that uranium, thorium, and radium, the three permanently radio-active substances thus far discovered, and the only ones which can with certainty be classed as elements, are the substances whose atoms are the three heaviest atoms known. Thus the atomic weight of uranium is 240, that of thorium 232, and that of radium 225. There is no other property in which these three substances are at all alike. In their chemical characteristics they are extremely different. Now, according to our modern mechanical theory of heat,

the atoms of all substances are in

extremely rapid rotation. It appears, therefore, that these rapidly rotating systems of heavy atoms such as characterize radio-active substances, not infrequently become unstable and throw off a part of their mass. The particles first projected are probably the Alpha-ray particles, and this process of emitting Alpha particles is probably the first stage of radioactivity. The mass left behind is itself unstable and throws off still other particles. The remainder, at least in the cases of thorium and radium, is yet again unstable, and still further particles are projected. We are actually able to follow the disintegration of the atoms through at least four (according to Rutherford, through five) successive stages. How many more stages there may really be, no one can certainly tell; but as soon as the stable condition is reached and no more particles are projected, the product has, of course, ceased to be radio-active, and its presence can no longer be detected by the delicate test of radio-activity. It is then only after it has accumulated in sufficient quantity to be capable of detection by the ordinary methodsnamely, by spectroscopic or chemical analysis-that it could be expected to be found.

The Birth of Helium

More than two years ago, Rutherford, with this picture of the mechanism of radio-activity in mind, made a prediction which has recently been most remarkably verified. The history of science scarcely affords a more striking instance of the fulfillment of scientif: prophecy. Since the element helium-which, by the way, was first discovered in the sun by means of a line in the solar spectrum that did not agree with the lines of any of our known elements, and which was found also on the earth only a few years ago by Lord Rayleigh and Professor Ramsay, the discoverers of argon-since this element helium is found in nature only in connection with radio-active minerals (that is, in connection with the salts of uranium, thorium, and radium), Rutherford predicted that helium would one day be found to be one of the ultimate products of the disintegration of the radio-active elements. About a year

later, as we have already seen, Rutherford himself found that the Alpha-ray particle had the same mass as the atom of helium. This pointed still more strongly to the confirmation of his original prophecy. Last July Professor Ramsay and Mr. Soddy actually saw the spectrum of helium grow out of the emanation from radium. This pointed to the apparently certain conclusion that helium is being continually formed by the disintegration of radio-active substances.

The Life of Radium

It appears, therefore, that all of the three heaviest atoms known are slowly disintegrating into simpler atoms, but the process is extremely slow. Despite the incessant projection of particles from radium so strikingly shown by the Crookes spinthariscope, no one has as yet been able to detect with certainty any loss whatever in the weight of radium or any diminution in its activity. Yet, unless the fundamental basis of all physical science is to be overthrown, we may be certain that it does both lose weight and in the long run decline in activity. From a knowledge of the amount of heat energy given off by one gram of radium per hour (the quantity of which the Curies and Laborde found to be 100 calories), and from the knowledge of the energy represented by each projected particle (this knowledge we possess since we know the mass and the velocity of the Alpha particles, the energy in the Beta particles being negligible compared with that in the Alpha)-from these data we can easily estimate how fast a gram of radium is losing weight and how fast it is losing activity by the disintegration of its particles. The result of the calculation indicates a period of probably not more than from 30,000 to 100,000 years when all the radium now in existence will have ceased to be radio-active, that is, will have ceased to be radium. The life of uranium and thorium would be a million or more times as long, since these substances are expending their radio-active energy at about only onemillionth the rate of radium.

The Transmutation of the Elements The discoveries we have attempted to describe in the preceding have indeed

thorium, and radium are thus slowly disintegrating, we cannot say. If any other of the known heavy elements, such as gold, lead, barium, and bismuth, are undergoing such a change, it is too slow to be detected even by the delicate test of radio-activity. It is, however, interesting to note that the only change of this kind thus far discovered to be going on in the structure of an atom is in some respects similar to the changes that are incessantly occurring in the organic world in the structure of molecules. the ordinary processes of decay, the more complex molecules are continually disintegrating into simpler ones, and in so doing are setting free the energy that was originally put into them when the processes of life first built them up into their complex forms. So the studies of the last eight years upon radiation seem to indicate that in the atomic world, as in the molecular, certain heavy, complex

By

atoms are tending to disintegrate into simpler ones.

The analogy suggests a profoundly interesting question. Is there any process which does among the atoms what the life process does among the mole-. cules, which takes the simple forms and builds them up again into more complex ones? It would be rash to attempt to give any positive answer to such a query; yet the fact that radium now exists on the earth, taken in connection Iwith the fact that the life of radium is short in comparison with the past ages of the earth's existence, certainly seems to point to an affirmative answer.

Subatomic Energies

The energy required to produce such changes from the simpler to the heavier atoms, and the equivalent energy set free when the heavier atoms disintegrate into simpler ones, are enormously greater than the energies involved in any of the ordinary chemical transformations. The disintegration of a gram of uranium or thorium or radium sets free at least a

million times as much energy as that represented in any known chemical change taking place within a gram weight of any compound substance. The experiments of the last eight years have marked a most notable advance in science, in that they have proven the existence of this immense store of sub

atomic energy. It seems highly improbable, however, that this energy can ever be utilized on the earth to serve man's economic needs, for thus far we know of but three substances that are disengaging it, and these are changing so slowly that the rate of evolution of energy is practically infinitesimal.

Radium may possibly prove to be of some practical value in the cure of disease, although it is too early yet to assert even this with assurance. But even though no practical applications of the discoveries of the last eight years should be found, radio-activity will have served what is surely one of the most useful of all ends-namely, that of enlarging our knowledge of the ways of

nature.

It is estimated that 41,300 locomotives are in use in the United States.

On the slope of the hill opposite the Philippine exhibit at the St. Louis Exposition, the Department of Agriculture. is having a map of the United States made that will cover five acres of ground. The various products of each state will be shown on this map.

A new central station being erected at Berlin, Ontario, is to be fitted with Westinghouse gas engines. The first installation will amount to 460 hp., comprising three 13 x 14 three-cylinder 125hp., and one II x 12 three-cylinder 85hp. vertical engines. These engines will be used to drive direct-current generators for furnishing city lighting, and will

operate on illuminating gas of 650 B. T. U. calorific value.

One of the latest contrivances for facilitating research in tropical waters is a glass-bottomed boat through which the investigator may look into the depths of the ocean. The Geographical Society of Baltimore has adopted these boats as part of its equipment for scientific and geographical investigation. This curious observation craft is about twenty feet in length, very wide of beam to insure steadiness, and resembles in appearance a large dory. In the center, a square well is built several feet below the bottom of the boat and also extends up into it. The walls of this well are painted black to reduce reflection and light, and the bottom of the well is covered with heavy plates of perfectly clear glass. Looking down into this well, with the light shut out by a rubber cloth thrown over the head, the observer can see clearly into the quiet depths of the sea.

I

THINK I am not overstepping the bounds of truth when I say that no other class of machine used in the every-day work of the machine. shop has been so perfected in construction or adapted in application to such a variety of work as has the milling machine.

As I look back to the days of my apprenticeship and compare the milling machines then in use with some of the modern types of universal and manufacturing machines, the changes that have taken place appear-and they really are-marvelous. Not only have the machines been improved so as to do work of greater range than before, but it is now realized that a greater variety of work can advantageously be done on them than was formerly thought possible.

For a time it was my duty to make the necessary tools, set up the machines themselves, and in quite a large number of instances gage the work done. The gages were made filing size—that is, the work was milled a trifle large and then filed to fit-because we were not educated to a degree where we thought it safe to try to mill the work to a fit, or to finish size. Perhaps, indeed, considering the condition of the machines then in use, it would not have been safe to attempt milling to size. It is now, however, the rule to mill to fit; and by milling to finish size, unless the shape of the piece be such as to render such a proceeding out of the question, we not only eliminate the costly operation of filing, but, as a rule, work can be machined more accurately than it can be filed.

Fixtures to hold the work to be machined, and cutters for removing the sur

plus stock and for shaping, are now designed to do work that twenty-five years ago would have been considered impossible on the milling machine. Today, however, we cannot afford to do it in any other manner. I have seen pieces of work that were being machined to size and shape on a planer at a cost of several dollars each, transferred to the milling machine and the work done more satisfactorily at a cost of cents.

Modern competition has rendered it necessary to reduce the cost of manufactured articles, while at the same time the wages of the workmen must be maintained. No one factor has been of greater importance in rendering this possible than the modern milling machine.

Not only has the machine been made heavier, the spindle enlarged, the length of the bearings increased, and the whole redesigned to allow of heavier cuts, faster feeds, and the production of more accurate work at less expense; but the different means of adjustment have been arranged in such a manner that, instead of the guesswork formerly necessary, the machine can now be adjusted in any direction, accurately, to within a fraction of a thousandth of an inch, thus saving valuable time and obviating great expense.

These changes have not been the work of a minute, nor of a year, but have been accomplished step by step, according as it has been found desirable in one shop and another to mill work formerly done in some other manner. Fixtures and cutters were made that would hold the work and cut it to shape, but it was then found either that the milling machine was too light, or the spindle power was not sufficient, or the feed was not strong enough