256 COREESPONDENCE. 



a strong English quarter ; on comparing its magnifying power with a 

 ^ incli made in 1843 by A. Ross (of 75^ angular aperture only, but a 

 most excellent glass), and using a B. ocular, I found the y^^- division 

 on the micrometer (when x 'lOO diameters) was exactly i of an inch 

 longer when magnified by the No. 7 than when the quarter was used. 

 The angular aperture of Beneche's lens is certainly not less than 95°. 

 And now for what I have been able to do with it. 



Pleurosigma anrjulatum mounted by Moller (which by the way is 

 much more robust than the species w^e find in England), stri« resolved 

 by direct light ; with oblique light and D. ocular, the peculiar arrange- 

 ment of the terminal strife were well shown. 



P. intermedium, striae easily seen by oblique illumination. 



Nitzschia sigmoidea, transverse strife very fairly distinct. 



Cymhella Ehrenhergii, the costse were easily resolved into com- 

 pressed beads, as were also the transverse markings on Synedra 

 robusta. Pinnularia peregrina, the fine transverse lines on the costsB 

 were plainly visible (the last three specimens were in balsam). This 

 glass also performs well with the binocular, both tubes being well 

 illuminated. 



The admirable performance of these glasses is remarkable, as they 

 have no adjustment, and the price in Berlin is 10 thalers ! ! ! 



Yours truly, 



Fred. Kitton. 



Powell and Lealand's |^th and ^th with straight 



Candle-light. 



To the Editor of the ' Monthly Microscopical Journal.^ 



York, October 7, 1874. 



Sir, — Your correspondent, Mr. Hickie, desires to know if any of 

 your readers can do with their ^th objectives what he can do with his, 

 that is, whether they can resolve the markings on ^^Pleurosigma 

 angulatum " in a perfectly satisfactory manner under certain severe 

 restrictions which he mentions. If, therefore, you will allow me, I 

 will briefly state how a ^th in my possession has behaved under these 

 limitations. 



But since he speaks of the performance of his Gundlach's ith, it 

 may be as well to inform you first how a similar power, likewise in 

 my possession, fared under the ordeal to which both were subjected. 

 My glasses were obtained from Messrs. Powell and Lealand, the eminent 

 London makers. 



The slide of " P. angulatum " selected was one covered dry for 

 ^'^g^th inch. This I placed upon the stage, and then brought the flame 

 of a composite candle to an exact level with it, and precisely in a line 

 with the tail of the compound body, mirror and diaphragm being both 

 discarded. The first frustule that appeared now stood out with such 

 clearness, and was so beautifully defined, that the whole proceeding, 

 when viewed as a testing operation, looked to me to be little better 

 than child's play. 



