84 H. L. Smith on the vegetable nature of Diatomacee. 
scope is now too well known to need any description here, The 
one I have used was made by Browning of London. It is not 
at all difficult to obtain a characteristic spectrum from a living 
diatom, a to compare it directly with that of a desmid, or 
other plan 
I need nat here give the results “ yom Suffice it that 
from about fifty comparisons of spectra, I can unhesitatingly 
assert that the spectrum of shloreigl 3 is identical with that of 
diatomin. 
The spectrum in question is a characteristic one, and is fig- 
ured below 
A very black, narrow band in the extreme red, reading at the 
lower edge, which appears to be constant, about 2 % of Mr. Sor 
by’s scale, is too characteristic to be mistaken. There are ‘ewe . 
other very faint bands, not easily seen, and somewhat more 
variable in position. The black ery in the red is always pres- 
ent, and is remarkably constant in the position of its lower 
edge. In making comparisons of spectra it is of the utmost 
importance that the slit of the spectroscope should be abso- 
lutely in the focus of the achromatic eye lens. If this be not 
attended to, there will be a slight parallax ; and bands really 
identical in ‘position, e.g., those of blood fuiariot cruorine), will 
not absolutely correspond when two spectra are formed, one 
om blood on the stage of the microscope, and the other "from 
the same on the stage of the eye-piece 
The dark band of the chlorophyl spectrum is slightly varia- 
ble in width—and the action of acids and alkalies sometimes 
the dead distommatle; almost identical in sales, with the fer- 
rous carbonate, so often found in bogs where the larger diatoms 
= abundant; and what is more remarkable, is, that the car- 
nate gives no absorption bands at all. As a general rule, 
alooholis solutions of chlorophyl and diatomin have the band 
slightly depressed, reading 1 to 1} on the interference scale. 
