418 SrsIiLiEY OP CUBEEXT EESZJLECHES KELATIS'G TO 



fault is it necessitates a verr quick convergence of the optical axis. 

 . . . With voung eyes and nominaUy sound this difficulty is not 

 distressing, but for older eyes it becomes annoyins. Always upon 

 looking up after using Wenham's binocular, for a while he had found 

 an unpleasant feeling of readjustment of the eyes to the normal con- 

 dition."'" He also thinks that " a trained eye would make out about 

 as well and with less trouble the acttial structure of any object under 

 examination with the monocular as with the binocular — at least such 

 was his own experience offere<i with much diffidence. For his own 

 special work with high power and wide angles they are not really 

 suited, but others engaged in another line of investigation requiring 

 only medium power and low angles may find them serviceable," 



Electric Light in Microscopy.* — Dr. H. Tan Hetirck describes 

 his exfieriments with the electric light, commencing by pointing out 

 that, notwithstanding the perfection of homogeneous-immersion 

 objectives, which show readily delicate details, it frequently happens 

 that the study of diatoms (particularly the small forms) gives con- 

 siderable trouble, as well by the difficulty of resolving the striae as 

 by the impossibility of counting them with a low power. It is 

 necessary, therefore, to have recourse to a high power, or even to 

 monochromatic light, which is not always possible, as the sun is fre- 

 quently hidden, j^rticularly in winter. He has, therefore, for some 

 time thought of the electric light for illumination with the Microscope, 

 and his exr.>eriments have demonstrated that the incandescent electric 

 light supplies the illumination par excellence which the microscopist 

 requires. 



The author then proceeds to treat of the production of the elec- 

 tricity, referring to the fact that in a probably near future the 

 inhabitants of large towns will have electricity distributed at their 

 doors, so that the necessities to be met will be principally those of 

 microscopists who live in the cotmtry or in small centres. Two 

 modes are at present open for the production of electricity, dvnamo- 

 electric machines and batteries. The former are, however, out of the 

 question for the purpose tmder consideration, a small battery being 

 capable of supplying all that is required at a small expense and Httle 

 trouble. 



As to the different forms of batteries the Bunsen is the most 

 powerful, but the vapours which it gives offi and other points, render 

 it unsuitable for microscopical purposes. In his original paper the 

 author recommended the Tommasi battery, a modification of the 

 former, as in every way preferable and cheaper, giving at the same 

 time a full and detailed description of it, with woodcuts. He has 

 since written us, however, that the battery of E. Eegnier is still 

 better and the Tommasi has been discard^. The former is thus 

 described in a supplementary note : — 



The Eegnier battery has modified Daniell elements with very 

 large surface. They consist of a narrow rectangular cell in copper 

 (45 X 23 X 5^ cm.) within which is a zinc plate, closely enveloped 



• Bull. Soc. Belg. Micr^ vii. (1882) pp. Ixii.-lxxiii. (3 figs.). 



