State of the Physical Sciences. 305 
They embody Seas ce reflections of a mathematical al pee at 
the advanced age of three score years and ten, Cha 
that there is sufficient evidence for the existence of ether and 
regarding gravity, or any other force varying ene distance, as an 
essential quality of matter, because, according to that principle, 
we must, in seeking for the simplest idea of hese force, have 
itself, in its quiescent ‘state, must have uniform densit y. t must 
be coextensive with the vast regions in which material force is 
displayed. Challis had prepared himself for the elucidation and 
defence of his pleat age theory by a profound study of the a 
of motion in e flui Suen the mathematical form 
which he has poet these laws 3 has attempted to jakin the 
principal experimental results in light, heat, aida electricity 
and magnetism. Some may think that Mr. Challis has done 
ether ps the atom. What e has written is the guide-post 
pointing the — in which othe is next to travel: but the 
end of the journey is yet a great way off. The repeated protests 
of Mr. Challis against the popular physics of the day, and his 
bold proc roclamation of the native, independent motion of the ether, 
prevents the free ether, asks the 
late Sir J ohn Herschel, from onpeneng into Petes space? Mr. 
ence can follow it, is a riya wi age e ‘source of the mo- 
Am. Jour. Sci1.—Tuirp slaty Vou. VIII, ee 46,—OcT., 1874. 
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