NEGATIVE MAKING 



81 



in Canada balsam, are practically invisible un- 

 der plain transmitted light, but, submitted to 

 the magic rays of the polariscope, present the 

 beautiful picture seen in the print, showing 

 the characteristic black cross of the starches 

 most superbly. The negative was made in 

 this manner : Objective, a Beck ro of moder- 

 ate aperture; ocular, none; condenser, none; 

 revolving diaphragm, medium-sized opening; 

 radiant, coal oil lamp, flat side of flame ; plate, 

 rapid landscape; exposure, 2% minutes; de- 

 veloper, pyrogallol; amplification, no diame- 

 ters. 



The beautiful effects of polarization in the 

 illumination of crystalline substances are shown 

 in Fig. 1 8, the subject being the flower-like 

 crystals of amygdalin. These are almost in- 

 visible under ordinary transmitted light, but, 

 submitted to that from the polariscope, are 

 seen in glowing colors upon a black ground. 

 The objective used in making negative was a 

 Beck first-class f, without eyepiece or con- 

 denser. Radiant, coal oil, flat side of flame; 

 plate, a medium landscape; exposure, 9 min- 

 utes; developer, pyrogalol; amplification, 70 

 diameters. These two negatives were made 

 nearly twenty years ago, and are in perfect 

 condition at present. 



