October 24, 1890.] 



SCIENCE. 



235 



and ^gsipated, so we do not see the same tail of a comet all the 

 time, because the matter which makes up the trail is constantly 

 streaming outwards, and constantly being replaced by new vapor 

 arising from the nucleus. The evaporation is, no doubt, due to 

 the h«at of the sun; for there can be no evaporation without heat, 

 and tke tails of comets increase enormously as they approach the 

 sun. Altogether, a good idea of the operations going on in a 

 comei will be obtained if we conceive the nucleus to be composed 

 of water or other volatile fluid, which is boiling away under the 

 heat •f the sun, while the tail is a column of steam rising from it. 



"We now meet a question to which science has not yet been 

 able to return a conclusive answer, — ' Why does the mass of vapor 

 always fly away from the sun?' That the matter of the comet 

 should be vaporized by the sun's rays, and that the nucleus should 

 thus be enveloped in a cloud of vapor, is perfectly natural, and 

 entirely in accord with the properties of matter which we observe 

 around us; but, according to all known laws of matter, this \apor 

 should remain ar-ound the head, except that the outer portions 

 would be gradually detached, and thrown off into separate orbits. 

 Thet« is no known tendency of vapor, as seen on the earth, to re- 

 cede from the sun, and no known reason why it should so recede 

 in the celestial spaces." 



The uniformity of nature justifies the inference that the ten- 

 dency of highly tenuous matter to recede from the source of heat, 

 here observed in the celestial space.», will certainly be found in 

 terrestrial matter when we reach the requisite conditions. The 

 first supposition of Mr. Crookes, namely, that the rays of heat ex- 

 erted a propelling force on the solid matter of the vanes in vac- 

 uum, has no analogy in the phenomena above described; but the 

 hypothesis that the rays of heat exert this force on the residual 

 gas in the bulb seems to be entirely in accord with what occurs in 

 the celestial spaces. TLe cometary matter, having become ex- 

 tremely tenuous, is put in motion in a direction radiant from the 

 sun, the source of heat. It was in the effort to find operative in 

 terrestrial matter the force which causes the projection of a com- 

 et's tail, that my attention was attracted to the consideration of 

 the cause of motion in the radiometer. 



Tlie tenuity of the matter in the bulb can be measured ; and it 

 would be interesting to know at what degree of tenuity the phe- 

 nomenon will appear, when it reaches the maximum, and when, 

 as perfect vacuum is approached, it disappears. It is evident that 

 the phenomenon results from the tenuity, and not from the tem;- 

 perature, of the residual gas: for a i-adiometer immersed in melting 

 ice and salt, andesposedtothesun, will revolve rapidly. Heatcauses 

 tenuity by expansion , and during this process heat is absorbed i but it 

 seeme from this determination, that, when a certain degree of tenuity 

 is reached, matter begins to lose its capacity to absorb heat by fur- 

 ther expansion, and then it develops the tendency to recede from 

 the source of heat, the tendency increasing with increase of heat 

 and tenuity. The work of pushing around the fly in the radiome- 

 ter requires a momentum which is the product of the impetus 

 and mass of the residual gas in the bulb; and, whether the mo- 

 tion be vibratory or tangential, it is possible to reduce the mass of 

 gas in the bulb to so small a quantity that no possible impetus 

 would put the fly in motion. 



The phenomenon of incandescence also seems to indicate that 

 matter reaches a condition of tenuity at which it begins to resist 

 further expansion. In his beautiful description of the phenomena 

 of combustion and incandescence in his '-New Chemistry," Pro- 

 fessor Josiah P. Cooke leaves no doubt that the incandescence in- 

 cident to combustion results from the resistance of matter to heat- 

 work. It is true that he does not refer to this as the cause of 

 incandescence, but he shows most clearly that ordinary heat- 

 work in matter is to produce chemical re-action or expansion, or 

 both: and, when these are free and unrestricted, no incandescence 

 appears; but when this work is resisted, incandescence results. 

 Vibratory motion always rasults from two forces, that is, from 

 force resisted; and, light being a form of vibratory motion more 

 intense than that of heat, it is certainly not improbable that the 

 light from combustion is the result of the resistance of matter to 

 the less intense vibratory motion of heat. Assuming this to be 

 true, we have a very simple explanation of the incandescence of 

 highly tenuous matter. The Geissler tubes, Crookes's tubes, Tyn- 



dall's tubes, and many other phenomena, demonstrate that highly 

 tenuous matter becomes incandescent from the application of 

 heat at a temperature far below that required for incandescence 

 in matter less tenuous; and the same thing seems to occar in a 

 comet's tail, which shines with a light of its own, and in the 

 aurora horealis. 



If it be true that when matter reaches a certain degree of tenu- 

 ity it begins to resist further expansion, we ought to expect it to 

 become incandescent at low temperatures, the temperature at 

 which the phenomenon would occur being determined by the de- 

 gree of tenuity. Professor Tyndall was not looking for this law 

 in his experiments, but they come very near demonstrating its 

 existence. 



The proijosition that matter at a certain degree of tenuity resists 

 further expansion, and for this reason, on the application of heat, 

 is put in motion in a direction radiant from the source of heat, and 

 becomes incandescent at low temperatures, does not involve a 

 denial of the molecular theory of matter, nor of the kinetic theory 

 of gases. The proposition is entirely consistent with the theory 

 that matter is composed of molecules, and that in the gaseous 

 form, or in any other form of matter, these molecules are in con- 

 stant vibration. It simply requires us to admit, that, if there be 

 molecules in vibration, the vibration, like every thing else in na- 

 ture, can go so far, and no farther. It does require us to deny 

 the deduotien from the kinetic theory to the effect that the vibra- 

 tions are infinite, and that if the molecules of gas " were in space, 

 where no external force could act on them, they would fly apart 

 and disappear in immensity." But this is a mere vagary without 

 legitimate parentage either in reason or experiment, and ought to 

 be discarded from physical science even if the proposition here 

 presented is not established. A much more serious objection to 

 the proposition will come from those who have accepted the mo- 

 tion of the radiometer as visible evidence of molecular vibration. 

 There is something intensely enticing in the idea that we have a 

 wheel revolved by these scientific elves, and the theory has4aken 

 deep root in the minds of scientists in this country and in Europe. 

 But the proposition here presented, if it can be scientifically 

 established, opens the way to determinations in respect to the 

 constitution of nature of far greater importance than any here 

 mentioned; and I earnestly hope that some competent scientist 

 will take up the subject, and continue the experimental work 

 until no doubt remains. Daniel S. Teoy. 



BOOK-REVIEWS. 



Harvard Historical Monographs. Edited by Albert B. Habt. 

 No. 1. The Veto Power. By Edward C. Mason. Boston, 

 Ginn. 8". $1. 



The study of history is now carried on quite extensively in this 

 country, and new works are constantly appearing: but we cannot 

 say that many of them have a very high value, while not a few 

 are almost unreadable. We are glad, therefore, to meet vi-ith a 

 work of the kind that is somewhat superior to the mass, and such 

 a work we have in this pamphlet by Mr. Mason. It has, indeed, 

 no particular excellence of style, but it shows more thought and 

 more political intelligence than is usually the ease with such 

 works The author has not only studied his facts with great care 

 and diligence, but discusses the principles involved, and often 

 with much acuteuess. He gives a brief chronological list of all 

 the bills that the Presidents of the United States have vetoed, with 

 an extended account of the more important ones. The body of 

 the work is divided into chapters dealing with the different classes 

 of vetoes, and showing their signiScance. The constitutional ques- 

 tions involved in the use of the veto power, and also its bearing on 

 party politics, are carefully noted ; and, though the author has con- 

 fined himself to the national government, his work will be of in- 

 terest and of real use both to students of history and to practical 

 politicians. This series of historical monographs has been well 

 begun, and we wish it good success; but we trust that the 

 writers will not conflne themselves to American history nor to the 

 history of politics, but will treat the whole subject of the past life 

 of humanity. 



