346 THE MICROSCOPIST. 



IMPROVEMENTS IN OBJECTIVES. 



A laudable desire to place really good objectives in the 

 hands of students at a reasonable price has led to great 

 emulation among opticians. Spencer, Tolles, Wales, Gund- 

 lach, and the Bausch & Lomb Company, in addition to 

 their most perfect objectives, both dry and immersion, 

 which must necessarily demand a high price, have pre- 

 pared others at less cost for professional and students' 

 use, which are worthy of all praise. Some of them fall 

 but little below the performance of the very best glasses. 



Test-objects, such as those referred to at page 56, and 

 which formerly required objectives of best workmanship 

 and highest power, are now resolved by a large number 

 of objectives. The J-inch of Spencer or Tolles, the ith of 

 Gundlach, and even a T 4 th of Bausch & Lomb, with proper 

 eye-pieces and illumination, will exhibit nearly all which 

 can be desired, yet powers of from Jth to T ' 6 th are still 

 better. For refined histological work 2 'gth or -^th, or 

 even ^gth inch (Tolles), will be found most useful. 



The desire to obtain the largest angle of aperture possi- 

 ble has, however, led to a reduction of the working dis- 

 tance, or the distance between the object and front of the 

 objective, so that only the thinnest covers can be used. 



For immersion objectives, also, a variety of fluid media 

 have been proposed, as glycerin, castor oil, oil of cedar, 

 and kerosene. 



IMPROVEMENTS IN EYE-PIECES AND AMPLIFIERS. 



Periscopic eye-pieces, consisting of a piano or double 

 convex field lens and an achromatic meniscus, have been 

 brought to great perfection by E. Gundlach and the Bausch 

 & Lomb Company. Solid eye-pieces by Tolles have also 

 found favor. I have made some improvement in field of 

 view and definition by substituting a meniscus for the 



