A. R. Grote—LEffect of the Glacial Epoch, etc. 335 
and the deflection produced on an ordinary astatic galvanome- 
ter noted. After experience this could be done with great 
accuracy. It might be better in some cases to have the coil 
slide over a limited distance on the tube, though, for the use I 
intend to put the results to, the other is best. 
p to 85° Qe is nearly proportional to the deflection ; and 
when any larger value is put down on the Tables, it is the sum 
of two or more deflections. I have not the data in most cases 
to reduce my results to absolute measure, but took to 
insure that certain series of experiments should be comparable 
among themselves. 
Having measured Q at all points of a rod, we may find Q by 
adding up the values of Qe from the end of the rod. 
€ magnetizing-force to which the bar was subjected was in 
taken to represent Q most nearly, and then the corresponding 
formule for Q- taken with the same constants. 
or ease in calculating by ordinary logarithmic Tables, we 
May put el—] (SSL 
[To be continued. ] 
Art. XLIIL—The Hfect of the Glacial Epoch upon the Distribu- 
hon of Insects in North America; by AuG. R. Grote, A.M. 
(Read before the American Association for the Advancement of Science, at 
Detroit, Oth.) 
From the condition of an hypothesis the Glacial period 
has been elevated into that of a theory by the explanations it 
afforded of a certain class of geological phenomena. The 
resent paper endeavors to show that certain zoological facts 
are consistent with the presence, during past time, of a vast 
pro; ive field of ice, which. in its movement from norh to 
south, gradually extended over lurge portions of the North 
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