448 EL. L. Nichols—Character and Intensity of the 
To lessen the chances of error I used, in addition to the gal- 
vanometer, Kitao’s* ‘‘ Leucoscope,” an instrumentt admirably 
adapted for showing qualitative differences in the character of 
heterogeneous rays. I used the original instrument described 
in Kitao’s treatise. The leucoscope is essentially a polarizer, 
resembling in some respects Soleil’s saccharometer. 
“N, N, (fig. 2) are two Nicol’s prisms, &, &, denote two 
2. 
Qs 
exactly similar rhombohedra of calcareous spar, g is a plate of 
mica, thin enough to show colors of the first order, is a slit, 
the width of which can be altered at pleasure by means of an 
such as to give a sharp enlarged image of the slit, and of dis- 
oh so 
observer rotates the ocular Nicol N,, the action of the mica lamina 
and of the quartz plates gives to the two halves of the double 
image different tints, alternating between red and green. What 
ever be the character of the ray, a thickness of quartz can be 
found such that at four positions of the ocular Nicol, distant 90 
m one another, the two halves assume the same neutral tint. 
_ Kitao calls this the point of maximum paleness. This thick 
ness of the quartz plates varies with the composition of the 
ray, and a means is thus afforded of detecting minute quali- 
tative differences in its light. When the experimenter, having 
adjusted the instrument for a particular kind of heterogeneous 
light, turns—without changing the quartz plate—to the observa" 
tion of rays which differ from those of the first source, he fin 
that the position of the ocular Nicol corresponding to the ma*- 
imum of paleness differs for each new kind of light. * 
A series of experiments were made to test the adaptability 
i * Diro Kitao, “ Zur F. ee ai * ane 1878. 
ee or Mew eaey ap nne pte ge ET 
ion is not so widely known as it deserves to be, I must refer for lack of spac? '0 
