Geology and Natural History. 75 
only twenty-five are useful in Roiniones the light. Thus os “ 
difficult to produce two or a greater number of arcs in the sa 
continuous curreut, since it is necessary to overcome the inverse 
electromotive force of each light. This fact is an objection to the 
use of batteries, Lave gs ous current machines, secondary batteries 
like those of Planté or of Faure. The conditions, however, are 
very different with oe use of alternate current dyna mo-electri ic ma- 
chines; for with a certain speed of alternation the effect of the 
inverse electromotive force i isa minimum. ‘The difference of tem- 
t 
e 
PERS apf edn, No. 18, Mae 
8. Stellar Photography.—In a letter se eho to M. A. Ciena 
H. Draper relates that he — — xt in ide aneare? alter 
fo 
14°1, 14-2, 14°7, according to the scale of Poyson. Photography 
has thus secured images of stars nearly at the ner of waibility 
in a telescope of nine inches aperture. It seems, therefore, not 
improbable that stars which are invisible to he. eye in a tele- 
pee of a size can be photographed.— Comptes Rendus, > 0. Pete 
ril, 188 
‘ Weat Ae Warnings.—Professor aga ee ed in 
lecture delivered at South Kensington, April 29, spoke of t 
probability that British magnetical weather ad be followed si 
ae pehe of Eleivicity. —M. Favre has modified the sectiadk 
pe nei of Planté by coating the lead plates with a covering 
miniu The sheets of lead are separately covered with 
pote aed rolled erethen | in a spiral with a layer of felt be- 
tween, and are then placed in a vessel of sulphuric acid and 
water. hen a current is passed into this cell the minium on 
one plate is reduced to metallic lead and on the other is oxidised 
to peroxide. When the cell is discharged this action is reversed. 
According to M. ian axl one of these spiral cells weighing 75 
kilograms can store up energy sufficient to furnish one horse 
power for an bout ss Nara May 19, 1881. a8 
Il. GroLtoegy AND NaruraAu Hisrory. 
1. Sketch of the ge Oe —. Columbia ; by GxoraE M. 
Dawson, D.S., A.R.S.M., —British Columbia includes a 
= portion of the Saree a oe Cordillera region of the west 
coast of America, which may be described as consisting here of 
