602 



SCIENCE. 



[Vol. I., No. 21. 



those that have made the acquaintance of a book, or 

 for those that have not ? For myself, I can answer 

 that I care most for the reviews of those books that 

 I have not seen. In conchision, [ wish to say that 

 Mr. Gage is a stranger to me, and I have never liad 

 any sort of communication witli him. Whatever 

 one mlglit say in his behalf, my remarks were not 

 made for his benefit, but to point out what I believe 

 to be one of the first duties of the reviewer of a 

 scientific book to his readers. S. T. M. 



Lexington, Va., June 13. 



[Tlie limited space at our command will not allow 

 of extended analyses of the many text-books of science 

 which are continually appearing. A short notice 

 either of their general merit or demerit is all we can 

 give. In the case of Gage's ' Elements of physics,' 

 the reviewer used the book as a text to preach 

 against the common custom of teachers in using the 

 atomic theory in their explanations as if we knew 

 definitely that atoms exist.] 



Solar constant. 

 Prof. C. A. Young has kindly called my attention 

 to an unintentional oversight in my article entitled 

 ' Solar constant ' (Science, p. 542). In the general 

 equation sent me by him, i represents 'degrees of 

 heat,' not 'quantity of heat;' and m represents 

 ' time,' not ' unit of time.' H. A. Hazen. 



A zoo-philological problem. 



On the New-England coast, where Mya arenaria is 

 abundant, and known as the ' clam,' an annelid which 

 is common in the same localities is called the 'he- 

 clam,' and is believed by many fishermen to be the 

 male of the moUusk. 



In Norway, Mya arenaria is abundant in the fiords 

 of the north. It has no economic uses; but its as- 

 sociate, an annelid, the 'piir' (said to be Arenicola 

 piscatorum), is an important bait, and gives its name 

 to the Mya which is called the 'piirschaal.' 



Why should the common annelid and the common 

 mollusk be thus associated in popular nomenclature 

 in remote regions ? It is interesting to observe that 

 the form possessing commercial value in each in- 

 stance gives its name to the one which is in lower 

 esteem. G. Beown Goode. 



The sun's radiation and geological climate. 



In my objecting (Science, p. 395) to the assump- 

 tion that the dissipation of solar energy from loss of 

 heat diminishes the supply of sun-heat received by the 

 earth, I said, that, so far as there has been any change 

 in the supply, it has been in the direction of an 

 increase, and hence cannot explain tlie undoubted 

 decrease in the temperature of the earth's atmosphere. 

 I think Professor Le Conte's criticism (Science, 

 p. .543), taken in its entirety, corroborates my position. 

 He shows that the quantity of heat incident normally 

 on a unit of surface in a unit of time varies as the 

 area of a great circle of the sun X heat-emitting 

 power of each physical point of the sun: hence the 

 quantity emitted would not increase, unless the heat- 

 emitting power increased faster than the square of 

 the temperature. He adds that " some physicists 

 (Rossetti) make the latter proportional to the square 

 of the absolute temperature, while others (Stephan) 

 make it as high as the fourth power." If Rossetti is 

 right, there has been no decrease in the amount of 

 solar heat received; while, if Stephan is right, there 

 has been a very great increase : for, on the assump- 

 tion that the temperature is inversely as the radius, 

 as stated in Professor Newcomb's article (Popular 



astronomy, p. 508), the heat-emitting power, if the 

 solar radius is reduced to one-half, will be increased 

 four times, and will just compensate for the great 

 circle being reduced four times in area. If the 

 emissive power increases, as Stephan claims, then a 

 doubled temperature will increase it sixteen times, 

 and, the area being diminished only to one-fourth, 

 the earth will receive quadruple the heat. 



It is true that the heat-emitting power of any 

 (solid) body varies according to the area of its surface, 

 providing all the other conditions are unchanged. 

 In case of solids and liquids, very little change can be 

 made in their density by any force that we can apply, 

 — so little, indeed, that no appreciable effect can be 

 produced ; but gases are easily affected, and there is 

 no difficulty in conceiving them reduced many times 

 in bulk. Now, suppose two spheres, e.g., of hydrogen, 

 of equal masses and of the same temperature, but 

 one having twice the radius of the other. They will 

 radiate equal amounts in equal times, as I shall try to 

 show. I assume that the radiation goes on only from 

 points of matter, — the atoms of the hydrogen. 

 Conceive each sphere made up of a vast number of 

 concentric layers, each one molecule thick. The 

 number of layers will be the same, and the number 

 of molecules in each will also be the same: con- 

 sequently the heat-emission of the outside layer will 

 be the same in both spheres. What would be true 

 of the first layer would be true of all, unless the 

 outer one intercepts some of the rays. So far as the 

 outer layer is gaseous and elementary (it is very 

 doubtful whether any chemical compounds can exist 

 in the intense heat of the sun), it is a vacuum to 

 radiant heat ; for Professor Tyndall, in ' Heat con- 

 sidered as a mode of motion,' has shown (p. 362) this 

 in reference to oxygen, hydrogen, nitrogen, and air, 

 and, in general (see rest of the lecture), that elemen- 

 tary gases or vapors produce little or no effect upon 

 the radiant heat that passes through them. It must 

 be remembered, too, that the source of heat employed 

 in his experiments was icy-cold in comparison with 

 the sun, and that the penetrating power of heat-rays 

 increases as the temperature of their source rises. 

 It is therefore probable that the heat from the lower 

 layers passes through the upper ones, so far as they 

 are gaseous, with little or no loss, and hence that 

 in gaseous bodies the heat-emitting power for any , 

 given temperature is proportional, not to the surface, 

 but to the mass or density. 



But suppose that diffused through the upper layers 

 were molecules that were capable of stopping every 

 ray that impinged upon them. Neither the absolute 

 number nor the size of these bodies would be affected 

 by shortening the radius, but only the space between 

 them. If the radius were reduced to one-half, the 

 apertures would be reduced in area to oric-fourth, 

 while the radiating molecules within any given dis- 

 tance would be increased eightfold: in other words, 

 the chances of not passing out into space would be 

 increased only four times, while the number of shots 

 would be increased eight times; so that, in tins case, 

 the heat-emissive power would be actually increased 

 by the condensation. If to this be added an increase 

 of the same power from the rise of temperature 

 (either as the square or the fourth power, Eosetti or 

 Stephan), there can, I think, be no doubt that any 

 change which has occurred in the earth's temperature 

 from the sun's losing energy has not been in the 

 direction of growing cooler. 



As a corollary of the above, I add, the radiant or 

 heat-emitiing power of a sphere of gas appears to be 

 a function of mass and temperature, and not of sur- 

 face and temperature. 



