ma... REPORTS FROM THE SECTIONS. 
Notes upon Tolles’s duplex front one-tenth immersion 
objective, and of a comparative trial of the same 
with Zeiss’s oil immersion one-eighth (No. 18), by 
both oblique and central light. : 
By H. Suarp. 
[Read before the Microscopical Section, 11 August, 1879.] 
Havine a few weeks ago received from Mr. Tolles, of Boston, a 
dry, immersion with water, or immersion with glycerine, withou 
change of front, the corrections for the different fluids being most 
perfectly accomplished by the use of the screw It isa 
duplex front or four system objective, and the screw collar has an 
unusual range of position, and the magnifying r varies con 
the objective is adjusted for glycerine and cover 008” to 009", the 
power with A eyepiece is quite 540 diameters ; with water immer- 
sion and covers from 004” to 008” the power is 470.to 500 
diameters. : 
: Used dry the performance of this glass in clearness of defini- 
used ; a Seibert’s dry jth of medium angle 135° which I have 
gives a slightly flatter field and greater working distance. Com- 
ta. : 
Sives superior definition, and in flatness of field is not inferior, 
— Powell and Lealand has a separate front and the 
rt. 
: has not. 
The Tolles (dry) will correct and work through a cover gauged 
007” provided the object is adherent to the cover, but has hardly 
any working distance for focusing into an object which has any 
thic » with covers 004” and 005”; there is good working 
: ; distance if the object is not very thick or in a cell. 
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