128 THE MICROSCOPE. 



this up or down, and the glass object-slide horizontally, the requisite 

 amount of movement is obtained to bring the object into the field. 

 The object being brought into view, the image is roughly adjusted on 

 the focussing-glass by sliding c on A j the focussing is completed by 

 aid of the fine adjustments, G, K, and allowance then made for the 

 amount of non- coincidence between the chemical and visual foci of the 



fig. 91. 



object-glass. The difference in each glass employed should be ascer- 

 tained by experiment in the first instance, and then noted. By em- 

 ploying a finely-ground focussing-glass greased with oil, this arrange- 

 ment forms an agreeable method of viewing microscopical objects with 

 both eyes, and is less fatiguing. As a very large field is presented to 

 the observer, this arrangement might be advantageously employed for 

 class demonstration. 



Two exquisitely delineated negative objects obtained in this way 

 by Mr. Delves were afterwards printed as positives, for the purpose of 

 illustrating an excellent paper on the "Application of Photography 

 to Microscopy," in No. 3 of the Quarterly Journal of Microscopical 

 Science. 



