32 ELEMENTS OF STATIC ELECTRICITY. 



But the researches of modern science have swept 

 away many of the errors of the past, and it is not im- 

 possible that Dr. Wollaston's demonstration may share 

 the same fate. Many eminent scientists, who have 

 made experimental investigations on the subject, hold 

 that the expansibility of the earth's atmosphere is 

 unlimited ; among whom may be cited Grove, Gassiot, 

 Geissler, and Dr. Andrews. And W. M. Williams, 

 in his work, " The Fuel of the Sun," claims to have 

 discovered a serious error in Dr. Wollaston's calcula- 

 tions, which vitiates his conclusion. 



The assumption of these writers is that an atmos- 

 phere, the same as that of our earth, pervades all 

 space ; that in the interplanetary spaces it becomes ex- 

 ceedingly attenuated ; and that each of the heavenly 

 bodies attracts and surrounds itself with a portion of 

 it ; the extent and density of which is in proportion to 

 the mass of the body. 



The high degree of vacuum which can now be attained 

 by improvements in the air-pump, seems to demonstrate, 

 that while electricity will pass more freely through rare- 

 fied air, on account of the reduced resistance, than 

 through air of ordinary density, it must still have a 

 medium in which to travel ; and that its passage through 

 an absolute vacuum, or space devoid of any known ma- 

 terial substance, is highly improbable. But as the best 

 attainable vacuum is still only an approximation to an 

 absolute vacuum, the full demonstration of this point 

 has not yet been reached. 



The existence then of some elastic medium, by which 

 the two forms of radiant energy, known as light and 

 heat, can traverse the interplanetary spaces, is not 

 questioned. Nor does the theory of the unlimited ex- 



