(321) 
THE SPECTEUM OF THE EUBY— A NEW CHAEACTEEISTIC 
TEST. 
By J. Mom, M.A., D.Sc, F.C.S. 
(Eead March 17, 1909.) 
On placing a ruby before the slit of a spectroscope, using strong 
illumination, preferably sunlight, a very remarkable absorption-spectrum 
is obtained, which differs from all others in resembling an ordinary 
emission spectrum. The light is cut off except for a sharp narrow red 
band situated just beyond the B line of the solar spectrum, and this band 
bears the closest resemblance to the potassium or lithium line as commonly 
seen in the Bunsen flame when a rather wide slit is used. The limiting 
wave-lengths of the band are about 6,915 and 6,945 tenthmetres. Its 
width is therefore about half its distance from the B line in the solar 
spectrum. The phenomenon is most easily seen in the pale rubies ; 
corundum with even the faintest pink shade generally shows the character- 
istic line ; but even the darkest true rubies show it if the illumination be 
strong enough. No other pink or red stone — pyrope, almandine, spinel, 
or tourmaline, for example — shows this line, which would therefore appear 
to be characteristic of the colouring of the true ruby. In addition to the 
red line the spectrum contains wide green and orange bands which are, 
however, not characteristic. 
