1900J MICROSCOPICAL JOURNAL. 113 



meet at a house in Hanover Square and pursue together 

 their microscopical studies. On May Ist, 1865, a notice 

 was published, suggesting the formation of an amateur 

 microscopical society that would cover ground untouched 

 by the Royal Microscopical Society. For this reason the 

 subscription was made as small as possible, and the club 

 itself was formed July 7, 1865. Since then the Club has 

 done good work for amatuer microscopy, and almost as 

 much for microscopy in general, and it still Nourishes. 



W.Watson's New ^inch Holoscopic Objective. — Two 

 new achromatic objectives by Messers. Watson & Sons, 

 were constructed on a new principle, having similar cor- 

 rections to the apochromatic lenses, and, like them, re- 

 quiring to be used with jjompensating or over-corrected 

 eyepieces for their proper correction. This enterprising 

 firm has now put out a lens which we can only describe as 

 a remarkable one. It is a half-inch of no less N. A. than 

 •65, which is equivalent to the very high optical index of 

 31-5. Its spherical and chromatic corrections approxi- 

 mate more cloiely than we would have believed possible 

 to those of the apochromatics. The finest dry lens at 

 present made is considered to be Zeias's apochromatic half- 

 inch, and Messrs. Watson's lens has the same power and 

 the same aperture. This in itself is in its way a distinct 

 achievement, as we know of only one other similar lens 

 which exceeds this aperture. But a very careful compar- 

 iBon between the new holoscopic lens and the apochro- 

 matic half-inch shows that even on the most difficult and 

 critical tests the achromatic is hardly surpassed by the 

 apochromatic lens. In spherical correction and in defi- 

 nition there is really little to choose between them ; but 

 the achromatic lens, as is to be expected, shows, on criti- 

 cal and suitable tests, a slight amount of outstanding col- 

 or that is absent in the apochromatic. The objective is 

 corrected for the 250 mm, (10") tube, and bears a 27 com- 

 pensating eyepiece most satisfactorily. The price is $17.50. 



