314 ON THE CHANGE OF REFKANGIBILITY OF LIGHT.
of it. The commercial name of the glass is canary glass. The following observations were made with a small bottle of English manufacture.
74. When the sun's light was admitted without decomposition the dispersed beam was yellowish green. The1 dispersion was so copious that when a large lens was used the dispersed beam approached to dazzling. The prismatic composition of this beam was extremely remarkable. The beam was found on analysis to consist of five bright bands, which were equal in breadth and equidistant, or at least very nearly so, and were separated by narrow dark bands. The first bright band was red, the second
t i reddish orange, the third yellowish green, the fourth and fifth
| j green. I have very frequently observed dark bands, or at least
{j f minima, in the spectrum resulting from the prismatic analysis of
dispersed beams, but I have not met with any example so remarkable as this, except in a class of compounds which the properties of canary glass led me to examine.
75. On analysing a beam of sunlight transmitted through a certain thickness of the glass, there was found to be a dusky absorption band a little below F, another less distinct at F^G,
»f and the spectrum was cut off a little below G.
li
'jfi 76. When the glass was examined by the third method, the
I, dispersion was found to commence abruptly about the fixed line b.
j It remained remarkably copious throughout the whole of the
,J visible spectrum and far beyond, with the exception of a band
i^| beginning a little above F, and having its centre at about F$Gt
i' where there was a remarkable minimum of activity. This band,
ji it will be observed, was situated between the bands of absorption
already mentioned. The tint of the dispersed light appeared to
•i be uniform throughout, except perhaps where the dispersion was
'j just commencing. This was the best medium I have met with for
| showing the fixed lines of extreme refrangibility, though some
others were nearly as good.
\ 77. On examining the glass by the fourth method, it was
/i found that the dispersion commenced nearly where the dispersed
I light ended, that is, the lowest refrangibility of the rays capable of
! being dispersed was nearly the same as the highest refrangibility