328 W. A. Norton—Molecular and Cosmical Physics. 
One of the most conspicuous of the theoretical positions 
reached, was that of the incessant operation of a repulsive 
force, exerted at all distances beyond the minute sphere of 
molecular attraction, upon individual molecules. Evidence of 
the operation of such a force at small distances, in the contact 
of bodies whether by pressure or impact, has often been recog- 
nized, and it has generally been conceived to be the physical 
cause of the elastic outward pressure of gases ;* but in both 
cometary and solar physics we have striking evidence of the 
operation of a force of repulsion upon the atoms of highly 
attenuated gases, at great distances. It is at present the gene- 
elief among astronomers that the tails of comets are com- 
posed of attenuated matter urged away to indefinite distances 
from the sun, by an energetic solar repulsion.t I think I may 
justly claim that my own researches, with reference to Donatis 
comet, have served materially to strengthen this conviction, 
long since entertained by such eminent astronomers as Olbers 
and Bessel. 
The outstreaming of luminous vapors from the sun’s photo- 
sphere, recognized by spectroscopists in the solar protuberances, 
and in the indefinite extension of the solar corona,} give mt 
mation of a highly energetic repulsion of subtile vapors from 
the sun’s luminous surface. 
Another position taken was that the contiguous molecules of 
a liquid mutually repel each other; the equilibrium bemg 
maintained by a compressive force exerted inward at the sur 
face—that to which the phenomena of capillarity are ascri 
Several striking experimental discoveries have recently been 
made, which furnish a strong support to this view. These at 
of gases, has its essential counterpart in the impulsive waves of heat nea 
proceeding from the molécules. Besides, the advocates of this theory oa he 
strained to admit the existence of a gaseous molecular repulsion, to account 10F 
elastic reaction of the molecules in their mutual collisions. ag 
+ See Herschel’s Outlines of Astronomy, eleventh ae pp. 382-3; Loomis 
; ) 237- 
Young, in his article on the Solar Corona (this Jour., May, 1871) oe 
be reconciled with the known smallness of the pressure at its Oe is 
ar below even that of hydrogen, or of matter whose ity 18 to 
annihilated, or even rendered negative by some such solar repulsion a8 at 
be operative formation of a comet’s tail.” The latter view is that W 
have long advocated. (See this Jour., Jan., 1871; and June, 1871, p. 406). 
ST eR S! Me RAEN vor ptr pk cueing esl +. Pe), | aerate 
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