APPLICATION OF PHOTOGRAPHY. 173 



the stage-plate, after the manner of Oberhauser's micro- 

 scopes. An index L is affixed opposite the graduated head 

 K. The stage and clamp slides vertically on H ; and by 

 sliding this up or down, and the glass object-slide hori- 

 zontally, 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 ; 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 object-glass. The difference in each glass 

 employed should be ascertained by experiment in the first 

 instance, and then noted. By employing a finely-ground 

 focussing-glass greased with oil, this arrangement 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," No. 3 of 

 the Quarterly Journal of Microscopical Science. 



