186 THE AMERICAN MONTHLY [June, 



Stand I tried their common l-4tli, 75° without correcting 

 collar ; mounted Navicula rhomhoides on quartz, saw 

 transverse lines with dull blue daylight and very mod- 

 erate oblique light. At night with more oblique light 

 and candle light saw longitudinal lines and with gas 

 light and still more oblique light saw lines." 



Continuation of experiments on actinic ray. May 2, 

 1866. To day being dark and rainy I thought it favor- 

 able to try the actinism of the light of a petroleum lamp. 

 With my Ij inch objective Wales and B occular, Zent- 

 mayer, took three negatives of a transverse section of 

 Nuphar stem as follows. 



A. 27.5 at 10 A. M., 5 minutes exposure, good. 



B. 57.5 at 10 A. M., 8 minutes exposure, good. 



C. 25. at 10^ A. M., minutes exposure, over exposed, 

 showing the large amount of actinism in the light of 

 the petroleum lamp. The large silvered reflector was 

 used behind the lamp, the lamp itself up close as possi- 

 ble to the object and the bull's-eye condenser between it 

 and the object, so that there were four thicknesses of 

 glass besides the objective and occular (1 chimney, 2 

 bull's-eye, 3 slide and 4 cover) and balsam between the 

 source of the light and the sensitive plate." 



This is all I have in memoranda in my record book 

 but there are many other experiments which I remember 

 and they were carried on for several years as I got a 

 chance up to the present time. I now have to record 

 what they have resulted in. 



I make a slide of mica colored blue with aniline blue 

 and this slide I place in the path of the illuminating 

 beam of light for the microscope. This is a true actinic 

 slide, but a slide can be made of glass also. The color 

 is put on by means of a varnish of gum Thus or any 

 other colorless varnish. A slide can be also made of 

 mica but this scratches easily. Besides the actinic slide 



