Tae MuicroscopicaL News 
AND 
NORTHERN MICROSCOPIST. 
No. 26. FEBRUARY. 1883. 
ON DR. CARPENTER’S ADDRESS.* 
By W. Biacxeurn, F.R.M.S. 
ACH member of the Society has, I believe, received a copy of 
the address which Dr. Carpenter delivered at Montreal in 
August last, to the Histological and Microscopical Section of the 
American Association for the Advancement of Science. For this 
we are indebted to Mr. Miles, who calls our attention, in an accom- 
panying letter, to certain passages having reference to “diatom 
tests” and “the best objectives for biological work.” 
There is much in the Address of which I think no microscopist 
will disapprove. Its general tenor, however, is to depreciate the 
value of lenses of wide aperture, and as we are now beginning to 
appreciate the true value of such lenses, owing to the researches of 
Prof. Abbe, I would direct your attention to some of the statements 
with which Dr. Carpenter is credited, as they appear to me to be 
inconsistent with observation and theory. The Doctor warns 
American microscopists that they are now “ going over the track 
which the English passed over twenty or twenty-five years ago, and 
have now abandoned,” because they “ found no valuable result to 
biological research.” If this statement is true, I think it ought to 
stand the test of a comparison of the apertures prevailing at that 
period with those in general use now. It must not, however, be 
overlooked that in Aigh powers immersion lenses are more fre- 
quently used now than they formerly were, and that a dry lens of 
175° has a smaller veal aperture than a water-immersion lens of 
97°, or a homogeneous-immersion one of 82°. The lens of widest 
aperture ever constructed in this country is a one-eighth, recently 
made by Messrs. Powell and Lealand, having an angle of 150° in oil 
(N.A. 1.47), and a resolving power 47 per cent. higher than a dry 
* Remarks made to the Manchester Microscopical Society on January 4th. 
VOL, III, 
