ward and admirably adapted to its purpose. Mr. Dole writes from the standpoint of the "liberal" Christian, with a and reverlarge-heartedness, candor

ence which will command the respect of those who are not in entire agreement with his reasoning. His book is helpful and inspiriting to an unusual degree, and should be widely read.

The thrilling and the picturesque are George Wharton well blended in James's account of his ten years spent "In and Around the Grand Canyon" of the Colorado, which Little, Brown & Co. publish. This wonderful gorge, unrivalled on our continent for scenery, is becoming as fascinating to the tourist as it has long been to the explorer and geologist; and Mr. James has shown excellent judgment in adding to his description of its structure, formation aud flora, and his history of the attempts, successful and unsuccessful, to explore it, some chapters of practical detail about present modes of approach, railroad connections, advantageous points of view, opportunities for the camera and the like; but the value of the volume as a guide book does not in the least lesthe general sen its attractiveness to reader. The narrative passages are sometimes of intense interest, and vivid bits of description are supplemented by illustrations-more than a hundred in number-many of them from photographs taken by the author himself, and all of high quality.

71

In his monograph entitled "Napoleon: the Last Phase" (Harper & Bros.), Lord Rosebery presents a picture of the great Napoleon at St. Helena which is alive with human interest and touched Precisely with a generous sympathy.

as a skilled photographer chooses the exact moment when the countenance of his subject is most truly self-revealing, Lord Rosebery has chosen the period in Napoleon's life when there was least masquerading, and when most of the true character of the man disclosed itself. To this circumstance we may attribute the fact that this brief and brilliant monograph gives a more vivid impression of the great figure which shook Europe and was magnificent even in desolation than many histories and biographies of portentous size. Through the narrative runs a manly indignation over the ineffable meannesses of Napoleon's jailers, and the petty persecution to which he was subjected. The fine analysis, acute generalizations and noble eloquence of the final chapters must deepen the regret of the reader that so splendid an historian as Lord Rosebery might have been has been spoiled in the making of an indifferently successful statesman.

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1

VOLUME X.

FROM BEGINNING Vol. CCXXVIII.

I. UNSUSPECTED RADIATIONS.

I.

The sensation created five years ago by the discovery of the Röntgen rays had hardly begun to subside, and the patient, minute exploration of the newly-opened field was only just beginning when new discoveries of formerly unsuspected radiations came to add to the already great complexity of the phenomena, upsetting the provisional generalizations, raising new problems, and preparing the mind for further discoveries of a still more puzzling character. At the present time the physicist has to account for not only the kathode and the X or Röntgen rays, but also for the "secondary" or "S-rays" of Sagnac, the “Goldstein rays," the "Becquerel rays," and, in fact, for all the radiations belonging to the immense borderland between electricity and light. Nay, most fundamental questions concerning the intimate structure of matter are being raised in connection with these investigations; and the physicist cannot elude them any longer, because one of his most important principles, established by Carnot, and generally recognized since, seems also to require revision, or has, at least to receive a new interpretation.

II. INSECTS AND MALARIA.

So many different "rays" are now under consideration that it is necessary to begin by well defining them in a few words, even at the risk of repeating things already said in these pages and generally known. The "vacuum tube" is the starting point for all new radiations, and in its simplest form it is as is known, a sealed glass tube, out of which the air has been pumped, and which has at each end a piece of platinum wire passed through the glass and entering the tube. When these two wires are connected with the two poles of an induction coil, or the electrodes of an influence electrical machine, or a powerful battery, they become poles themselves. The tube begins to glow with a beautiful light, and a stream of luminous matter flows from its negative pole the kathode-to the positive pole. These are the "kathode rays," the detailed exploration of which was begun years ago by Hittorf, but won a special interest when Crookes took them in hand, and once more when the Hungarian Professor Lenard began to study them in the years 1893-95. It is evident that the glass tube may be given any shape that is found convenient for some special purpose, and that the degree of exhaustion of air (or of any other gas with which the vess*

was filled before exhaustion), the forms and the disposition of the two poles, as also all other details of construction, may be varied at will, according to the experiments which are intended to be made. Now, if such a tube be placed inside a black cardboard muff which intercepts its light, and if it be brought into a dark room near to a screen painted with some phosphorescent substance, this substance begins to glow, although no visible light is falling upon it. If a wire be placed between the tube and the screen, its shadow appears on the screen, and if the hand be placed instead of the wire, dark shadows of the bones, but almost none of the flesh, are projected; a thick book gives, however, no shadow at all; it is transparent for these rays. Some radiations, proceeding along straight lines, must consequently issue from the tube and pass through the cardboard muff. Like light, they make the phosphorescent screen glow, move in straight lines (as they give shadows), and decompose the salts of the photographic film; but they are invisible and pass through such bodies as are opaque for ordinary light. These are the X or "Röntgen rays."

Various secondary rays originate from them. If the Röntgen rays meet a metallic mirror, they are not reflected by it, but simply diffused-that is, thrown irregularly in all directions; and, although they do not pass through metals, as a rule, they may be made strong and penetrating enough to pass through thin metallic plates. But in both cases they will acquire some new properties which will depend upon the metal which has diffused them or through which they have passed. Some new radiations will be added to them, and these radiations were named "secondary rays," or "S rays," by M. Sagnac, who discovered them. On the other hand, if kathode rays have been passed through a perforated metallic plate, they also get altered, and in this

case they will sometimes be named "Goldstein rays." And, finally, there is a wide set of extremely interesting (also invisible) radiations emitted by phosphorescent substances. They were discovered by H. Becquerel, and are named now "Becquerel rays," or "Uranium rays." More will be said of them presently.

This is, then, the world of radiations, the very existence of which was mostly unsuspected five years ago, and which have to be explained-the difficulty being in that they link together the Hertzian waves which are now used for wireless telegraphy, the visible light, the invisible radiations in the ultra-red and the ultra-violet parts of the spectrum, to so-called "actinic" glow of various substances placed in the violet portion of the spectrum, and many other phenomena. Light, electricity, magnetism and the molecular movements of gases, liquids and solids-all these formerly separated chapters of Physics have thus been brought into a most intimate connection and huddled together by these wonderful radiations.

Thousands of most delicate experiments have been made, and hundreds of papers have been written, during the last five years, in order to determine the properties and the constitution of these different sorts of rays. Various hypotheses have been advocated, and yet scientific opinion is still hesitating, the more so as new discoveries are made all the time, and they show that we are not yet the masters of the whole series of phenomena brought under our notice. Upon one point only-and a very important one a certain consensus of opinion begins to be established, namely, as to the kathode rays. Most explorers, including Lenard,' begin to be won to the idea that the kathode rays are the paths of very minute particles of matter which are thrown at a very great 1 Annalen der Physik, 1898, vol. lxiv. p 279.

speed from the surface of the kathode and are loaded with electricity. Even under ordinary conditions, when an electric discharge takes place between one metallic electrode and the other, under the ordinary atmospheric pressure in a room, we see that most minute particles of the metal are torn off the negative electrode (the kathode) and are transported in the electric spark. Molecules of air join in the stream, creating the well-known "electric wind," and the air-path of the electric spark becomes electrified to some extent, the more so when the discharge takes place in the extremely rarefied medium of a vacuum tube.' In this case the molecules of the rarefied gas, as also the metallic particles joining the current are transported, at a much greater speed, and we see them as a cone of light.

3

That kathode rays are real streams of particles of matter seemed very probable already in 1896, when the subject was discussed in these pages. Recent researches tend to confirm more and more this idea. They act as a real molecular or atomic bombardment, and they heat the objects they fall upon; thus, a thin lamella of glass which is placed in their path will be molten. It is also known from Crookes's experiments that when a little mill is placed so as to receive them on its wings, it is set in motion; and a back-current seems to be originated at the same time, as has been demonstrated by Swinton." They are deflected from their straight path by a magnet and are twisted along

4

I chiefly follow here Professor J. J. Thomson, who has explained his views in several articles (Philosophical Magazine, October 1897, vol. xliv. 5th series, p. 293; 1898, vol. xlvi p. 528; 1899, vol. xlviii p. 547. Also Nature, 1898, vol. lviii p. 8; 1900, vol. lxii p. 31); and also Dr. L. Zehnder, the author of a Mechanik des Weltalls (1897), in his address before the Freiburg Natural History Society in 1898.

3 "Recent Science," in the Nineteenth Century, March 1896.

the lines of force. Besides, a weak electrostatic force has upon them the same effect, showing that they are electrified negatively. Perrin and others who followed him have proved that these rays carry negative electricity with them. If they are taken out of the vacuum tube in which they originated to another tube, and are made there to fall upon an electroscope, they discharge it. Negative electricity cannot be separated from them; it follows with them when they are deflected by a magnet; it is their property-not some-thing added to them.

Moreover, it was already noticed by Crookes, and confirmed since by Professor Thomson, that most of their properties do not depend upon the nature of the gas-air, oxygen, hydrogen, etc.-with which the tube was filled first, and of which a minute quantity always remains in the tube. They appear as a property of matter altogether rather than a property of this or that gas. And when attempts were lately made to measure the sizes of the particles which are carried in the kathode rays, it was found that they are extremely minute-much smaller than the probable size of atoms-while the charges of electricity which they carry with them are relatively great.'

All these facts have brought Professor J. J. Thomson to the conclusion that the matter which is carried in the kathode rays, is not ordinary matter, such as we know it in our every day chemical experience, but matter in a state of a high dissociation. We know that the

4 Golstein's researches into the compound nature of the kathode rays and their effects deserve a special notice. They are published in several issues of the Annalen der Physik for the last few years.

Swinton, in Philosophical Magazine, 1898, vol. xlvi p. 387; Broca, Comptes Rendus, 1899, vol. cxxviii p. 356.

• Annalen der Physik 1898, vol. lxvi p. 1.

7 J. J. Thomson, Philosophical Magazine, vol. xlvi p. 528.