130 



TESTING THE MICROSCOPE. 



a more recent one, which left the factory in the year 1867. The 

 objectives of Hartnack examined date from 1860-64, as also those 

 of Beneche. On the other hand, Mueller's measurements refer to 

 objectives of Beneche, which were presumably constructed between 

 1868-71, while those of Hartnack correspond to about the same 

 year as ours. The only exception to this is No. 14 Imm. which is 

 one of the prize specimens of the Paris Exhibition. The objectives 

 of Gundlach (with the exception of N"o. 8 Imm., which is of an 

 earlier year,) date from about the years 1868-71 ; those of Zeiss 

 partly from 1864, partly from 1869-70 ; and those of Moeller from 

 1869. 



The objectives are arranged according to their focal lengths ; those 

 with correction-adjustment are marked " Corr." ; the immersion 

 objectives " Imm." The latter were all supplied with the correction- 

 adjustment. 



