648 



SUMMAEY OF CURKENT RESEAECHES RELATING TO 



Bansch and Lomb Optical Co.'s Condenser. — The speciality of this 

 condenser (fig. 167) is that one end of the cross arm has a weight acting as 



Fig. 167. 



a counterpoise to the bnll's-eye lens at the other end. Tne lens is 3 in. 

 in diameter. 



Miles' "Desideratum" Condenser.* — Mr. J. L. W. Miles' condenser 

 " consists of a plano-convex lens of given dimensions, having a ground spot 

 in the centre ; to this can be superadded an adjustable plano-convex lens of 

 short focus. These can be used with or without a system of stops and 

 discs with openings by means of a sliding spindle, which enables any size 

 or character of stop to be placed close under, or at any distance from the 

 lenses. 



" The following is a recapitulation of the working capabilities of the 

 condenser : — ■ 



"The back lens, used as a simple condenser for all powers, will be 

 found to meet all the requirements of the ordinary microscopist. With a 

 1/2 in. objective of 70° or 80° aperture, and a C eye-piece, P. angulatum 

 can be ' dotted ' readily. 



" Used as a combined condenser and light-modifier, it possesses advan- 

 tages superior to the devices in common use. 



"Asa dark-ground illuminator, it leaves nothing to be desired, working 

 easily with powers from 3 in. to 1/2 in. of 40° inclusive ; and also with the 

 4 in. by increasing the size of the spot-stop. 



"It gives binocular vision with 1/4 in. objectives, illuminatiug both 



* Trans, aatl Anu. Kep. Mauclicstcr Micr. Soc, 1886, pp. 31-3. 



