109 
of Edinburgh, Session 1866-67. 
held in a vertical or even inclined position, and examined by trans- 
mitted light, a current of fluid, without colour, will be seen issuing 
from the margin of the film, moving quickly to different parts 
of its circumference, sometimes dividing itself into two currents 
dancing opposite one another, and then extending into secondary 
currents in constant motion. Similar currents are produced upon 
various alcoholic solutions and a large number (seventy to eighty) 
of volatile oils, &c. 
If we now examine the film by reflected light, the principle and 
secondary currents will be seen as before, but accompanied with 
systems of coloured rings of great beauty, shifting their place on 
the film, sometimes in rotation, expanding and contracting quickly, 
and changing their form and colour. 
In small films there is often only one system of rings contracting 
and expanding with a constant variation of the central tint. In gene- 
ral, however, there are two, three, or several systems— each system 
being produced by a secondary current giving motion to the colour- 
ing matter on the surface of the film. In some cases the motions 
and colour disappear, the film becomes colourless, and tints issue 
from its margin as on the soap-bubble; but, in general, the film 
bursts before this takes place. The colourless currents and the 
colours into which they expand are supposed by the author to have 
the same origin as those upon the soap-bubble. The paper is illus- 
trated with drawings of the currents and of the systems of rings. 
3. Note on the Action of Nitric Oxide, Nitrous Acid, and 
Nitrites on Haemoglobin. By Arthur Gamgee, M.D., 
F.R.S.E., F.C.S. 
When engaged, during the course of last summer, in the exami- 
nation of the action of various medicinal and poisonous agents on 
blood, I observed the remarkable change in the colour of the blood 
of animals poisoned with nitrite of amyl. In every case in which 
I induced death by this agent the blood presented a dirty choco- 
late coloration, instead of the characteristic colour of normal blood. 
When examined by means of the spectroscope, this blood was found 
to present optical characters very different from those of ordinary 
blood, for the two well-marked absorption bands of 0 - haemoglobin, 
or (as the readers of Professor Stokes’ paper will know them better 
