_ 
Rh. D. Irving—Divisibility of the Archean. 237 
machine and by the Daniell cell, S and 8’, the respective 
oe rand 7’, the radii; n and n’, the number of coils in 
€ two galvanometers, and H the horizontal force of magnetism : 
__ 22n'S'H 
Baek: 
* pa2775H _ 1, 
a 
S'n'r 
cos a or S= —-— cos a@ 
n 7 
veh strength of the current from the dynamo is thus simply 
ined in terms of the current from the standard Daniell cell, 
Jefferson Physical Laboratory. 
Arr, XXXIIL.—Divisibility of the Archean in the Northwest ; 
by R. D. Irvine. 
[Extra ; 
ct from Address as retiring President of the Wisconsin Academy of Sciences 
December 30th, 1884.] 
é ‘ccompanying sketch-map (p. 240). 
‘ ag facts upon which the arguments and conclusions of this paper are based 
ven in vol. iii of the Geology of Wisconsin, which includes an 
in the Penokee District of _ Wisconsin by Professor 
per. 
map which was used in connection with the address, and from which this 
o inches to the mile. In reducing 
| Bteatly it 7 as drawn on a scale of _ 
it is difficult to illustrate all of the points spoken of. Dates map is designed 
istributi way. 
