OF VIEWING CERTAIN OF THE DIATOMACE^. 



207 



very beautiful l-8th (angular aperture 126°), made for me a 

 few months ago by Powell and Lealand, I was astonished to 

 find a field perfectly clear and white, and the illumination 

 little, if at all inferior, to that produced by Gillet's con- 

 denser, or the one I generally use myself, which was made 

 for me by Smith and Beck. The first object I tried it with 

 was Pleurosigma angulatum (the Naviciila angulata of 

 Quekett), which after a little trouble I was enabled to exhibit 

 most beautifully in dots ; and two experienced friends. Dr. 

 Branson and Mr. Gregory, in common with myself, were much 

 struck, not only with the very beautiful manner in which the 

 object was shown, but also with the rapidity with which 

 the adjustment could be effected. 



An experienced artist, Mr. C. J. Fleming, has carefully 

 sketched, from my microscope, the actual appearance of the 

 objects shown with this peculiar illumination, which at once 

 places in the hands of every student a ready and very cheap 

 method of exploring a field abounding with objects of the 

 most wonderful forms, and the internal structures of which, 

 as organized living beings, cannot fail amply to repay the 

 most diligent research. 



These drawings, most beautifully engraved by Mr. Tuffen 

 West (PI. XIII.), will show the student what he has to look for, 

 and so far as I know they give a better representation of these 

 beautiful objects tlian any yet published ; for however well 

 calculated the plates in the works of Quekett, Pritchett, or 

 Smith, are to show the forms of the different Diatomacece, they 

 fail, to my eye, to do justice to the wonderful appearances 

 actually exhibited by these shells. Perhaps it should be added 

 that the glass I generally use is an eighth, constructed by 

 Powell and Lealand ; with a l-5th of Smith and Beck, or a 

 l-4th of Ross, the markings may also be very well seen. The 

 light was obtained from the very complete gas lamp of Mr. 

 Highley. 



In order to show these olrjects in a satisfactory manner, 

 the most careful manipulation is required ; they must be 



