Physics and Chemistry. 111 
em between zero and 4°50. Proceeding thence to more exact results, 
¢ arrived at last at the conclusion that the electro-motive force sought 
was 1°82; that of Duaniel’s battery being 58; 100 representing the elec- 
864, 
: b) 
the microscope has been considered jusuly as the greatest improvement 
has advanced one step further, and, as it appears to me, in the only right 
direction to give complete satisfaction. Ihave lately received from him 
a binocular eye-piece, which is, as far as I can at present judge, every 
. We 
the best hitherto devised. The only instrument of this form I have had 
an opportunity of examining was a first class one by Smith, Beck & 
by reflected and direct vision; how far this was accidental Iam unable 
to say, as I had no opportunity to examine the prism. The slanting tube, 
ared to me awkward, and the reflected ray had 
to travel a longer path than the direct one; moreover, the use of a draw- 
tube for micrometry had to be dispensed with, as no longer length of 
draw-tube could be allowed than sufficient to adjust for different distances 
of the eyes of observers. Perhaps this is not a very serious objection ; 
culties 
. 
Yet it is an objection. The binocular eye-piece meets all these di 
ed so fi 
With the higher powers, as is the case with Mr. Wen m’s arrangement, 
_ ®ome care and special apparatus are required to bring out the full etfect, 
equally illuminate both fields. I have found that the ordinary achro- 
fat, oudenser, stopping out the central rays and using the plain side 
of the reflector, or better a reflecting prism, and the bull’s-eye condenser, 
