ELEMENTARY PHOTO-MICROGRAPHY. 



47 



and most brilliant effects from the light at our 

 disposal, though even then the direction of the 

 light passing through the bull's-eye is all-important. 

 A very small movement of the combined lamp and 

 bull's-eye has been known to reduce the exposure 

 one-half, because the rays of light had not previously 

 been concentric with the axis of the microscope. 

 Several good lamps with bull's-eye attached 

 can be bought, but an equally efficient arrange- 

 ment may be made, as shown in sketch (fig. 15). 



nr 



FIG. 14. FIG. 15. 



Fig. 15 shows a simple wood frame having a 

 circular hole for a paraffin lamp, and a slot in 

 which a tube carrying the bull's-eye may slide to 

 and from the lamp. The two end supports are free 

 to rise and fall, and are secured with screws when 

 the centre of the flame is brought to the height 

 of centre of microscope. 



A metal chimney is preferable to glass, but if 

 clear glass, then a shade with an opening on one 

 side to drop over the tube is desirable. 



