116 GLACIAL PHENOMENA. 
If I write 5+2,/— 1, it cannot equal any real number. 
If I write it equal to something, the statement is absurd : 
Whether I write 5+2,/— 1=v 29 
or 5 — 2,/-1=4/29 
each is a mathematical falsehood. But let me combine 
the two by multiplication, the imaginaries disappear, 
and I have the truth, 29=29. 
Untruths need to be handled carefully to get truth 
from their combination. If I had added the two 
pseudo-equations together, or had subtracted one from 
the other, the result would be false, for 10 does not 
equal 2,/29, nor does 4yV—1=0. If I take impos- 
sible quantities and perform upon them an impossible 
operation, the result may be a real, and, consequently, 
atrue one. It therefore need excite no surprise that 
in the hand of a master such expressions as /—1 
or/—a* “—1, should yield real quantities. 
FEBRUARY 26, 1889—SEVENTIETH REGULAR MEETING. 
Charles B. Warring, Ph.D., chairman, presiding ; 
twelve members and fifteen guests present. 
Professor William B. Dwight, Ph.D., read a paper on 
‘¢ Glacial Phenomena.”’ 
This paper called attention to some of the more recent 
views of glacial phenomena, founded upon the latest ob- 
servations. 
Two points of special importance were presented : 
1. The fact that Canadian geologists have been gener- 
ally inclined to assign the phenomena of glaciation, as 
observed by them, to floating ice ; pointing, for instance, 
to similar phenomena annually occurring in the mighty 
spring flood along the banks of the St. Lawrence River. 
On the other hand, the geologists of the United States 
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