THE DEFICIENT RAYS IN THE SOLAR SPECTRUM. 
455 
of lateral to central light increased, I continued to examine the whole length of the 
spectrum ; but I particularly fixed upon three parts of it for more accurate compa- 
rison, — the neighbourhood of the line B in the red, the beautiful system of lines 
between E and b in the green, and the group marked G in the indigo. Notwith- 
standing the diminution of light I had no difficulty in pursuing my observations 
during the annular period ; and at no time could I perceive any difference in the 
number, position, or thickness of the dark bands. I conceive that this result proves 
decisively that the sun’s atmosphere has nothing to do with the production of this 
singular phenomenon. 
Nor need this result surprise us. Spectra from artificial flames present bright and 
dark bands occasionally, without giving us any reason to suspect absorptive action ; 
and the electric light presents its proper dark rays * *. The solar light may also be 
primitively incomplete. 
Had the weather proved unfavourable for viewing the eclipse, I intended to have 
tried the experiment by forming an image of the sun by using a lens of long focus, 
stopping alternately, by means of a screen, the exterior and central moiety of his rays, 
and restoring the remainder to parallelism by means of a second lens, then suffering 
these to fall upon a slit as before. The result of my experiment during the eclipse 
seemed however so decisive as to no marked change being produced at the sun’s 
edges, that I have thought it unnecessary to repeat it. 
As I do not intend to prosecute this subject at present, if the experiment just 
described should seem to the Royal Society worthy of being recorded, I should feel 
honoured by this slight communication receiving a place in the Philosophical Trans- 
actions. 
scope of only thirteen lines in diameter. His prisms, no doubt, were very perfect, but these may be replaced 
by hollow prisms filled with highly dispersive oils. I have frequently used oil of cassia, but on the present 
occasion preferred Dollond’s flint glass, because the oil of cassia affected the distribution of colours in the 
spectrum, and was not otherwise very superior. I may observe in passing, that by viewing the direct solar 
light from a narrow slit by the naked eye, placed at some distance behind a good large hollow prism filled with 
oil of cassia, a very great number of the lines may be admirably seen. I take this opportunity of adding my 
anxious wish that Sir David Brewster should publish the details of his laborious experiments on the consti- 
tution of the solar spectrum, and his new maps of the solar lines. 
* Above a year ago I made some careful experiments on the spectrum produced by the oxyhvdrogen blow- 
pipe directed upon lime. I was then unable to detect any irregularities of illumination. 
Edinburgh, 2]st May, 1836. 
