19; 



NOTES AND CORRESPONDENCE. 



On tlie Microscopes in the International Exhibition In 



the English department there are about one-and-twenty 

 exhibitors of microscopes and microscopical objects or appa- 

 ratus, and it will be interesting to inquire how far, and in 

 what directions, improvements or novelties have been intro- 

 duced in these matters since 1851. Upon the whole, a very- 

 great advance is observable. Firstly, in the general style, 

 as it were, and elegance, arising from the accurate adjustment 

 of parts to their purpose, and in the various proportions of 

 the instruments. Secondly, the observer will be struck 

 with the numerous specimens of binocular microscopes, 

 mostly on the construction of Mr. Wenham, to whom micro- 

 scopists are so much indebted for the great improvement 

 thus introduced in the production of a really efficient 

 binocular instrument, so long a desideratum among opticians. 

 Thirdly, a striking feature in the microscopes of late con- 

 struction more especially, is the great attention that has been 

 paid to the mode of illumination of objects. The various and 

 ingenious ways in which this important object is carried out, 

 are well worthy of remark. Fourthly, in the construction of 

 object-glasses a marked advance in one direction, at all 

 events, has been manifested in the period that has elapsed 

 since the last Exhibition — this is in the amplification of the 

 apertiu'e, and the improvement thus affected in the definition 

 and detection of minute surface-marlcings. The utmost limit, 

 perhaps, has been reached in this respect, and it is very 

 creditable to our opticians that they should have so far suc- 

 ceeded in arriving at the limits of perfection. But at the 

 same time it cannot be denied that for really practical pur- 

 poses, in most cases, object-glasses of less aperture than those 

 which can now be made are far more serviceable. The great 

 object Avith opticians should be to produce object-glasses of 

 moderate aperture, and the s'hortest possible focal distance, so 

 as to place in the hands of the anatomist and physiologist a 

 really useful lens of the highest possible magnifying power, 

 and yet with a capacity of penetration which is incompatible 

 with an extremely wide aperture. 



