492 



SCIENCE. 



[N. S. Vol. VIII. No. 198. 



checked except by gravitation, -would be 

 sufficient to project a body from the earth 

 permanently into space. Even at a temper- 

 ature very close to absolute zero the new 

 gas would have sufficient molecular velocity 

 to escape from the atmosphere. 



Again, inasmuch as the molecular veloci- 

 ties of gases vary inversely as the square 

 roots of their densities, it follows from our 

 assumption of its molecular velocity that 

 the density of the new gas is only the ten- 

 thousandth part that of hydrogen, as shown 

 at the head of column 3. This is the hun- 

 dred and forty-four thousandth part the 

 density of air. It is generally believed that 

 the gases of the atmosphere distribute 

 themselves in the long run, each as though 

 the others were absent. Hence the new 

 gas must extend a hundred and forty-four 

 thousand times as high as the heavy con- 

 stituents of the air to bring about the same 

 proportionate reduction of pressure, even 

 if gravitation remained constant at all dis- 

 tances from the earth ; but the restraining 

 influence of gravitation on the expansion 

 of the atmosphere diminishes as the square 

 of the distance from the earth's center in- 

 creases. 



It is evident, therefore, without a math- 

 ematical demonstration, that the new gas, 

 being present in the atmosphere, must ex- 

 tend indefinitely into space without great 

 loss of pressure. This is only another way 

 of stating the result of its assumed molecu- 

 lar velocity. Now, there is no doubt that 

 the new gas exists in the atmosphere, though 

 probably in very small proportion, perhaps 

 much less than a millionth. Hence it seems 

 really probable that it not only extends far 

 beyond the atmosphere, but fills all celestial 

 space at a very small pressure. In recog- 

 nition of this probability, I have provision- 

 ally named it ajtherion, or etherion, mean- 

 ing 'high in the heavens.' Its symbol will 

 naturally be Et. 



I am aware that strong objections may 



well be raised to the hypothesis of an inter- 

 planetary and inter-stellar atmosphere ; but 

 I can see no escape from the conclusion I 

 have drawn, if I am not mistaken in my 

 premises. 



The estimated relative specific heat of 

 etherion appears at the head of the fourth 

 column, based again on the assumed relative 

 molecular velocity. In estimating the spe- 

 cific heat, I have not made it inversely 

 proportional to the density, as would be re- 

 quired by Dulong and Petit's law, giving a 

 value ten thousand times that of hydrogen; 

 but have used the formula suggested by 

 Professor Risteen in his work on ' Molecules 

 and the Molecular Theory,' which requires 

 that the product of the specific heat and 

 molecular weight of gases shall vary with 

 the number of degrees of freedom of their 

 molecules. I have assumed as probably 

 true that etherion is monatomic, with atoms 

 possessing only three degrees of freedom. 



Of course, the values I have estimated 

 for the molecular weight, density, specific 

 heat and molecular velocity of etherion 

 are intended only to indicate the ordei- of 

 magnitudes we may expect to find on fur- 

 ther investigation ; and it must not be for- 

 gotten that they are based on two assump- 

 tions : first, that the heat conductivity of 

 etherion is 100 times that of hydrogen ; and 

 second, that the ratio of heat conductivity 

 and mean molecular velocity is the same 

 for all gases. As before indicated, I expect 

 to find the heat conductivity of etherion 

 much higher than the value here assigned 

 to it. If so, the real value of its other at- 

 tributes will be still more startling than 

 those here given. The second assumption, 

 while by no means proved, seems at least a 

 good ' first approximation ' to the relation 

 between heat conductivity and molecular 

 velocity in gases. 



There is some evidence that etherion is a 

 mixture of at least two different gases. In 

 the course of my experiments I have met 



