1. That the atom, hitherto considered the smallest division of matter, can be broken up into corpuscles.

2. That these infinitesimally small particles are probably the material out of which all matter is constructed.

3. That radium may be converted into helium; i. e., that the transmutation of elements may take place and actually has occurred.

The statement has been made that X-rays are emitted by a highly exhausted bulb subjected to an electrical discharge. But their existence is found to be dependent upon other rays which are also connected with the discharge. These bear the name of cathode rays, because they originate at the negative electrode of a tube when in operation.

For several years the nature of cathode rays was the subject of much dispute. Some thought that they consisted of streams of minute, negatively charged particles shot off with enormous velocities from the cathode, while others maintained that they were waves in the ether, similar to light. From proofs furnished by Perrin and J. J. Thomson, physicists are now agreed in regarding cathode rays as negatively charged particles whose mass is only about one onethousandth that of the smallest atom known, hydrogen.

Professor Millikan says:

"Experiments upon cathode rays have proved conclusively that under some circumstances particles do exist which are smaller than the ordinary atoms of chemistry. It was the study of cathode rays, then, which first sounded the death knell of the indivisible atom of our earlier chemistry and prepared for the discoveries, which were soon to follow, of subatomic transmutations which involve the liberation of stored up energies, the very existence of which had never before been dreamed of."*

At the time of Roentgen's discovery many scientists thought that the X-rays. were simply cathode rays which had passed through the bulb. There are two distinct

* Popular Science Monthly, April, 1904.

deflected in the slightest degree by a mag

net or charged body and (2) they do not impart negative charges to bodies coming under their influence. It is generally agreed that these rays are ethereal rather than material in nature.

The question now naturally arises: Do radioactive substances emit rays similar to cathode or X-rays? At first it was suspected that the radiations from uranium, thorium and radium were similar to X-rays for the reason that they possessed the power of passing through opaque objects and of affecting a photographic plate. When the tests were applied which differentiate Roentgen from cathode rays, it was found that the Becquerel rays emitted were deflected, as shown by the distortion of photographs and that they had the power of imparting negative charges to surrounding bodies. It seems therefore that radioactive substances emit rays which are similar to cathode rays.

The

In 1899 Professor Rutherford of McGill University discovered that radioactive. substances gave forth other rays. alpha, beta and gamma rays have been distinguished.

The alpha rays do not have great penetrative powers and are stopped by a layer of air a few millimeters thick. They carry positive charges of electricity, for they are found to be deviable in the same direction, while under the influence of a magnet, as particles carrying a positive charge. Their mass is approximately twice as great as that of the hydrogen atom, or about the size of the atom of helium.

The beta rays are the cathode rays given off by radioactive substances.

The gamma rays are gifted with extraordinary penetrative powers. Apparently they are similar to Roentgen rays, if they are not actually the X-rays themselves. These rays carry no electric charges, for they are not deviable under the most powerful electromagnets. It is con

jectured that the gamma rays are ethereal pulses.

Whence comes the energy which is represented in the projected particles in the ultimate form of heat and light? This ceaseless emission is not caused by chemical changes. No alteration in the activity of radioactive substances is produced by extremes in heat or cold. Radioactivity seems to be as inherent a property of the atom of radioactive substances as is weight. itself. The change, whatever it may be, which is responsible for the expulsion of the various particles must involve a change in the nature of the atom itself.

Professor Rutherford in writing upon this subject, says:

"The evidence, as a whole, is strongly against the theory that the energy is borrowed from external sources and, unless a number of improbable assumptions are made, such a theory is quite inadequate to explain the experimental facts. On the other hand, the disintegration theory, advanced by Rutherford and Soddy, not only offers a satisfactory explanation of the origin of the energy emitted by the radio-elements, but also accounts for the succession of radioactive bodies. On this theory, a definite, small proportion of the atoms of radioactive matter every second become unstable and break up with explosive violence. * The energy radiated is, on this view, derived at the expense of the internal energy of the radio-atoms themselves.":

* *

*

In a paragraph entitled "The Disintegration of the Atom of Radioactive Substances," Professor Millikan writes:

"Discoveries seem to prove conclusively that the atoms of radioactive substances are slowly undergoing a process of disintegration, this disintegration being indicated, first by the fact that there is a continuous projection from them of particles of matter, the alpha and beta rays; and second, by the fact that we are able to detect the presence of new and unstable types of matter accompanying the phenomena of radioactivity. But just why these atoms are disintegrating and just how these new types of matter are formed must of course be largely a matter of speculation. Nevertheless, discovery has gone far enough to enable us to form a reasonably plausible hypoth

* Present Problems of Radio-activity, Popular Science Monthly, May, 1905.

esis as to the probable mechanism of radioactive changes. In presenting this hypothesis the first remarkable fact to be noted is that the three permanently radioactive substances thus far discovered, namely uranium, thorium and radium are the substances whose atoms are the three heaviest atoms known. Thus the atomic weight of uranium is 240, that of thorium 232, that of radium 225, or, according to recent spectroscopic test, 256. There is no other property in which these three substances are 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 not infrequently become unstable and project off a part of their mass. Those particles which are projected first are found to be the alpha particles, and the process of projecting the alpha is the first stage of radioactivity. The mass which is left behind, the uranium X, the thorium X or the emanation, according as the original atom was uranium, thorium or radium, is itself unstable and projects still other particles. The remainder, at least in the case of thorium and radium, is still unstable and another particle is projected. Thus we are able to follow the disintegration of the atoms through four or five successive stages.* The life history of these substances is tabulated as follows:

Sir William Ramsay, the emanation from radium, which was of the nature of a heavy gas, entirely vanished in the course of a month giving rise to the final product, helium. Helium is gaseous in nature and satisfies the court of last appeal, that of spectrum analysis, as to its being an element.

Mr. Rutherford made bold to prophesy that helium, since found only in connection with radioactive minerals, would be found one day to be one of the ultimate products of the disintegration of the radioactive elements. He writes upon this point the following:

"It is very remarkable that the gas helium, recently discovered by Sir William Ramsay, is only found in radioactive minerals. For this and other reasons it was suggested two years ago, by Mr. Soddy and myself, that helium might be a disintegration product of the radioactive elements. A few months ago this suggestion could not have been considered more than a justifiable speculation, which might possibly be put to proof in the next decade. But the progress of science is so rapid and its methods so powerful that it seems as if this question were answered in the affirmative to-day. Sir William Ramsay and Mr. Soddy have recently found that helium is present in the gases liberated by solution in water of a small quantity of pure radium bromide. The quantity of helium present was very small, but was sufficient to show clearly the characteristic spectrum of this gas. When the emanation was collected in a small vacuum tube and an electric discharge passed through it, a spectroscopic examination revealed some new bright lines which they considered were due to the emanation. In addition the spectrum of helium made its appearance and increased in brightness for several days. This remarkable result indicates that helium is a true disintegration product of the radium emanation."*

Since helium appears to be the final component in the disintegration of radioactive substances, it is probable that the views and calculations of scientists as to the lengths of existence of the sun and of the earth must be changed. Whatever view may be taken of the problem of the age of the earth, there can be no doubt that the dis

*The Disintegration of Radioactive Elements. Harper's Monthly, January, 1905.

covery of the distribution of radioactive matter in the earth throws grave light. on the validity of these calculations based on the assumption that it is a simple cooling body and tends to show that the present internal heat will be maintained for a much longer interval than was at first supposed.

The experiments of the last ten years. have marked a wonderful advance in science in that they have proved the existence of an immense store of subatomic energy. Even if radium and radioactive substances never find a practical application they will have served their end in enlarging man's knowledge and in deepening his insight into the nature and constitution of

matter.

POETRY FOR CHILDREN

MAE E. SCHREIBER

Poetry is the language of emotion. We should read poetry to feel more. The story poems appeal to the emotions. A man is a better man for reading poetry. All reading should be for the joy and pleasure that there is in it.

The folklore poems have in them some of the deepest philosophy of the day.

Some think that you can teach patriotism by sitting down and thinking about it. When there are two poems equally good I always pick out the one that is more musical.

I know of no way that will tend to make a child hate poetry than to make him tear it to pieces in studying it.

I've heard literary men say that Robert Louis Stevenson's poems were not poetry, that they were just doggerel; but Oh, how the children love them!

I'll read a poem to the children today that will make them cry, next day a poem that will make them laugh, then I will read a poem that will make them hate, and then a poem that will make them bend this hate a little so as to hate the right things.

who have little to spur them on to enthusiasm besides their love of profession, but if you don't enthuse you will be miserable and your work will be drudgery, and certainly you cannot expect an advance in your salary.

What has all that got to do with drawing from the object? Everything. Get interested yourself. Impart your enthusiasm to your pupils and you are bound to succeed. When you place a model before your pupils do not tell them what they see. Let them look and tell you with their pencil. There is infinitely more merit in earning a dollar than in having one given to you. Let the children make errors if they will and then show them where they are wrong.

A perspective drawing is one that represents distance forward or backward as well as up and down, and right and left. It is a drawing that represents distance in.

In the drawing of the leaf there were but two dimensions to represent. So there was no perspective. If the leaf had been curled over or bent there would have been three dimensions to represent. Quite a different affair I can assure you.

In my next communication I will endeavor to clearly define perspective and explain the fundamental laws governing it.