147 
Monochromatic Violet. By J. William Gifford. 
Yon have before you a photograph of Podura taken in this way 
(plate I. tig. 7) which is not bad. But it is not nearly so good as the 
two following (plate I. figs. Sa and h) taken with the malachite-green 
screen. 
In concluding, I want to draw your attention to methyl-green. 
It will give as good results as malachite-green and transmits so little 
red and ultra-violet, that for all except the most exact work, it can be 
used without the blue glass. A cell containing a glycerin solution 
of methyl-green may be made up with two thin cover-glasses and a 
metal ring only. Such a screen is very light, very thin, and will not 
break with any ordinary amount of knocking about. 
