( 13 ) 
IY. — Further Remarks on Tolies' lih and Poivell and 
Lealand's Immersion f%th. 
By Edwin Bicknell, Cambridge, Mass. 
On page 225, vol. vi., of tbe ‘ Monthly Microscopical Journal,’ I 
made some “ Remarks ” on Dr. Woodward’s “ Note ” in the number 
for September preceding. In the number for January, 1872, vol. vii., 
page 28, Dr. Woodward says that I have “ wilfully ” misinterpreted 
liis ‘published measurements of the wet front of the Powell and 
Lealand T Vth. I have not misinterpreted the actual power of the 
above-mentioned objective, although Dr. Woodward’s published mea- 
surements may look so exact — on paper ; and in order to make out 
my case I shall not go beyond Dr. Woodward’s own statements and 
“ published ” work, except in one case, to obtain my evidence. 
On page 29, vol. vii., Dr. Woodward gives a table of measure- 
ments of different objectives from Powell and Lealand, both wet 
and dry : I wish to state here that I have nothing to say in regard 
to any of the dry fronts , and only with regard to one immersion 
•j^th, and that one is No. 2. I assume this to be the one from 
the magnifying power as given in the table agreeing with Dr. W.’s 
published measurements. 
Dr. Woodward quotes from Mr. Charles Stodder * that “ob- 
jectives are named when adjusted for uncovered objects, a fact not 
generally known by purchasers. The power increases, that is, the 
focus is shorter as the collar is turned to work through the covering 
glass.” This is the method which I have used during the past two 
years, and I consider it the most certain and reliable. 
During the past winter Mr. Stodder has loaned me the glass 
positives of Amphipleura pellucida, which were made at the Army 
Medical Museum, with the Tolies’ ^th described by Dr. W. in his 
“ Note,” and also the positive made with the Powell and Lealand T Yth 
at the same time. These positives are marked precisely like those 
described by Dr. W. in his “ Note,” and are probably duplicates of 
those sent to the Editor of this Journal by Dr. Woodward. I have 
carefully and repeatedly counted the lines in the positive made by 
the Tolies’ ith (without eye-piece at 48 inches distance from the 
object to the screen). The length counted is exactly 4th of an inch 
(the reason of this will be seen farther on), and in this space I find 
just 74 (seventy-four) lines, making 37 0 lines to the inch in the 
positive. Dr. Woodward gives the fineness of the lines on the 
Am. pellucida at 95,000 to the inch. Dividing 95,000 by 370 
gives 256 -f diameters as the power of the objective at 48 inches 
distance, which is just what Dr. W. has marked the positive. 48 
divided by 256 gives T875, making the objective at that position of 
* ‘ M. M. J.,’ Oct. 1871, p. 208, note. 
