SOME PEOGRESSIVE EXAMPLES 287 



that a roughly defined image of the illuminant is projected 

 approximately in the position of the front lens of the 

 objective, the object occupying a position within the apex 

 of the illuminating- cone. 



Camera-extension, 3 ft. 6 in. 



Plate, Edward's Isochromatic (extra rapid). 



Exposure, 30 seconds. 



Development, metol-hydrokinone, somewhat restrained by 

 the addition of a few drops of a 10/ solution of bromide of 

 potassium to ensure a black-and-white result. Such an object 

 may be regarded as of the easiest type, and is eminently suitable 

 for a beginner. 



PLATE II, FIG. 3. Spine of an Echinus, x 40. 



Unstained preparation. 



Objective, 1-inch achromatic, by E. & J. Beck. 



No ocular. 



Camera-extension, 3 ft. 2 in. 



Small tube of black paper slipped into body-tube of micro- 

 scope to prevent reflection from the internal surfaces. 



Dark-ground illumination obtained by putting a stop of 

 suitable size at the back of the achromatic condenser, the top 

 lens of which had been removed. 



Illumination by Welsbach incandescent gaslight, the source 

 of light being placed about eight inches from the sub-stage 

 condenser. 



No colour-screen. 



Ilford ordinary landscape plate. 



Exposure, 2 minutes. 



Development by pyro-soda, the utmost contrast being 

 secured by using an excess of pyro, and about 10 / less than the 

 normal quantity of carbonate of soda. 



PLATE II, FIG. 4. Section of Human Scalp, x 75. 



Preparation stained with haBmatoxylin and methylene-blue. 

 Objective, K. & J. Beck's |-inch achromatic. 

 No ocular. 



No sub-stage condenser. 

 Illumination by a round- wick oil lamp. 

 Nelson's achromatic bull's-eye projecting an image of the 

 source of light on to the specimen. 



