Ba 
336 | J. LeConte on the Descent of Glaciers. 
when the contractile force becomes suffiggent to pull the upper 
It follows, therefore, that if the connecting rod is heated and then 
allowed to resume its former temperature, both of the bodies will 
descend the plane by an amount equal to the whole linear elon- 
gation of the rod. This will be repeated as often as there are oscil- . 
lations of temperature, until step by step, they reach the bottom. 
suppose the A 
and subject to extension 
rom increase of tem- 
CB will descend, and 
the rest CA will ascend ; 
the point C where they : 
separate being determined by the condition, that the force requi- 
site to push CA up the plane is equal to that required to push CB 
down it. When contraction takes place, the converse of the above 
will be true. The separating point D will be such, that the force 
requisite to pull DB up the plane is equal to that required to pull 
down it. DB is obviously, in this case, equal to CA in the 
other. Under these conditions, the determination of the lengths 
of the parts CA=DB and CB=DA, becomes a simple mechanical 
problem, from which Mr. Moseley deduces the formula, 
tan2 : ’ 
2=4L(1— ant), (1), in which, 
z=CA=DB 
L=length of rod AB 
t=angle of inclination of plane 
a=limiting angle of resistance. 
Let c be the elongation per linear unit under any given increase 
of temperature ; then the distance which the point B will be made 
to descend by this expansion, 
=c(CB 
=¢e(L—z) 
tan? 
By (1) =HLe(1+ 
tana 
If we conceive the bar now to return to its former temperature, 
contracting by the same amount (c) per linear unit; then the 
point B will by this contraction be made to ascend through the 
space 
=¢(DB)=cr 
a 
