594 



itGIENCE. 



[N. S. Vol. IX. No. 225. 



recall the fact that there is a still older name 

 which is in all respects available. This is 

 Leidy's Merycoidodon, having for its type M. 

 culbertsoni (Proc. Acad. Sci., Phila., 1848, p. 

 47). Professor Cope has rejected the name on 

 the ground that it is a nomen nudum; but a 

 generic name is hardly nudum when it is sup- 

 ported by a well-defined species and is, more- 

 over, clothed with two pages of description. 



Merycodus is another of Dr. Leidy's names 

 which must be restored to its rightful position. 

 This was proposed in 1854 and had for its type 

 species M. necatus. On the supposition prob- 

 ably that this name is pre-occupied by Owen's 

 Merycodon, it has been ignored. But it is in- 

 correct to assume that any two names ending in 

 odus and odon, but alike in other respects, clash 

 with each other. As to their forms they are 

 different enough to prevent confusion. As to 

 their derivation, as has been suggested to me 

 by my friend Dr. Leonhard Stejneger, of the U. 

 S. National Museum, they are unlike ; odus be- 

 ing the Latinized form of the Greek odoif, while 

 odon comes from the Ionic o6uv. The accept- 

 ance of this view will relieve us of the necessity 

 of rejecting, on philological grounds at least, 

 either word of many such couples as Menodus 

 and Menodon, Cosmodus and Cosmodon. 



O. P. Hay. 



THE FUNDAMENTAL LAW OF TEMPERATURE 

 FOB GASEOUS CELESTIAL BODIES. 



It has been long known that an isolated ce- 

 lestial mass of gas rises in temperature as it 

 radiates heat and contracts. Dr. T. J. J. See 

 [^Astronomical Journal, February 6, 1899 ; At- 

 lantic Monthly, April, 1899] points out that the 

 temperature of such a mass of gas is inversely 

 proportional to its radius, provided the mass 

 does not receive accretions of meteoric matter 

 and provided the gas conforms to the laws of 

 Boyle and Charles. When, however, the vol- 

 ume of the gaseous body is very great large 

 quantities of interstellar gases and particles 

 would fall into it and the first condition would 

 fail ; and when the gaseous body contracts to 

 small volume it would, perhaps, be far from a 

 perfect gas in its properties, so that the second 

 condition would fail ; to say nothing of the 

 probable dissociation and polymei'ization of the 



gaseous constituents due to the great changes 

 of temperature which, no doubt, take place. 



The suggestion of Dr. See that nebulous 

 masses are extremely cold is very plausible, in 

 view of his ' new law,' which 'may be assumed 

 to regulate the temperature of every gaseous 

 star in space,' but it is certainly contrary to the 

 indications of the spectroscope ; for nebulae 

 surely are approximately in thermodynamic 

 equilibrium in their smaller parts, if anything 

 in the universe is ; if so, there is no known 

 agency, electrical or other, which can cause 

 them to give off persistently abnormal radia- 

 tions. Radiations (wave-length) are as inti- 

 mately associated with temperature as are 

 molecular velocities, although both may be tem- 

 porarily abnormal in a given substance ; for 

 example, the velocities of the particles of a gas 

 in a vessel may be made to deviate momentarily 

 from Maxwell's law ; a cold substance, such as 

 calcium sulphide, may shine for a while after 

 exposure to sunlight, and a gas in a vacuum 

 tube may remain phosphorescent for a time as 

 the disturbing influence of an electric discharge 

 dies away. But it is hard to think of a certain 

 cubic foot of nebulous matter, surrounded for 

 millions upon millions of miles with similar 

 matter, remote from intense radiant centers, 

 still giving off abornmal radiations after odd 

 millions of years. Of course, such may be the 

 case, but Dr. See's law, in all probability, has 

 nothing so do with nebulse at all. There is no 

 physical reason why a nebulous mass might 

 not be intensely hot, held together (if, indeed, 

 we must assume it to be a gravitational unit) 

 by the gravitation of refractory nuclei and re- 

 ceiving continually from space as much matter 

 as it throws off, because of the high molecular 

 velocity of its gaseous parts. 



Dr. See's derivation of his law of tempera- 

 ture is incomplete and confused. It is based 

 upon the assumption, which should be definitely 

 proven, that the function which expresses the 

 density in terms of the radius coordinate r re- 

 mains of the same form as the external radius p 

 diminishes ; and he confuses pressure per unit 

 surface and pressure between given portions of 

 matter. Assuming the invariance of the density 

 function Dr. See's formula may be derived as 

 follows. Let p be the radius of the gaseous 



