546 PROFESSOR STOKES ON THE CHANGE OF REFRANGIBILITY OF LIGHT. 
and rapidly with the refrang-ibility of the rays incident upon it. Hence we are led 
to the conclusion that a strong electric spark is excessively rich in invisible rays of 
extremely high refrangibility. Glass is opake with respect to these rays, but quartz 
transparent. 
219. It is known that the phosphorogenic rays of an electric spark, at least those 
which affect Canton’s phosphorus, pass very freely through quartz, but are stopped 
by a very moderate thickness of glass. This alone, after what has been already 
mentioned, would lead us to suppose that the phosphorogenic rays coming from 
such a spark are merely rays of very high refrangibility. If so, they ought to be 
intercepted by a very small quantity of a substance known to absorb such rays with 
energy. 
After having made some experiments on the production of phosphorescence in 
Canton’s phosphorus by means of an electric discharge, and observed liow the in- 
fluence of the discharge was transmitted through quartz and stopped, or almost 
entirely stopped, by glass, I felt confident that my own observations were comparable 
with those of others. A small portion of the phosphorus was then placed on card, 
covered by an empty quartz vessel, and had the discharge of a Leyden jar passed 
over it. The phosphorescence was powerfully excited, being* visible in a room which 
was by no means quite dark ; and when the card was carried into a dark place, the 
phosphorescent light remained plainly visible for a good while. The experiment was 
then repeated with a fresh portion of the same phosphorus, the vessel this time con- 
taining water. The phosphorescence was produced as before, though not I think so 
copiously. But on taking a fresh portion of the phosphorus, and substituting for 
water a very dilute solution of sulphate of quinine, the influence of the spark was 
arrested, and the phosphorus was not rendered luminous. It was found that a solu- 
tion containing only about one part of quinine in 10,000, with a depth of half an inch, 
was sufficient to prevent the generation of phosphorescence. 
220. This result, it seems to me, would be sufficient, were proof wanting, to show 
that no part of the effect is attributable directly to the electrical disturbance. The 
effect produced when the phosphorus is at the distance of an inch or so from the 
points of the discharger seems exactly the same as when it is nearer, being merely 
somewhat weaker, as would naturally be expected, whatever view were taken of the 
nature of the influence. But at the distance of an inch, the influence of the spark, 
though it passes freely through quartz and water, is cut off by adding to the water 
an excessively small quantity of sulphate of quinine. It cannot be supposed that the 
electrical relations of the medium, or its permeability to electrical attractions and 
repulsions, are utterly changed by such an addition; while, on the other hand, the 
result is in perfect conformity with what we know respecting the stoppage of radia- 
tions by absorbing media. However, the principal object of the experiment was not 
to confirm the view which makes the influence of the spark to consist in the rays 
W'hich emanate from it, a view which I suppose is pretty generally adopted, but to 
