1822.] Philosophical Transactions for 1822, Part I. 379 
nomena, especially with respect to mercury artificially cooled, 
and in vapours from comparatively fixed substances. 
The diminution of the temperature of the torricellian vacuum, 
to as low as about 20°, appeared to diminish its power of transmit- 
ting electricity ; but between 20° above and 20° below zero, the 
lowest temperature that could be produced by pounded ice and 
muriate of lime, the power seemed stationary, and nearly the 
same as that of the vacuum above tin. “ At all temperatures 
below 200°, the mercurial vacuum was a much worse conductor 
than highly rarefied air.” : 
« It is evident from these general results,” the author conti- 
nues, “ that the light (and probably the heat) generated in elec- 
trical discharges depends principally on some properties or 
substances belonging to the ponderable matter through which 
it passes; but they prove likewise that space, where there is no 
appreciable quantity of this matter, is capable of exhibiting 
electrical phenomena; and, under this point of view, they are 
favourable to the idea of the phenomena of electzicity being pro- 
duced by a highly subtile fluid or fluids, of which the particles 
are repulsive, with respect to each other, and attractive of the 
particles of other matter.” 
To this succeed some further observations on the nature of 
electrical phenomena and their relations, which are terminated 
by a remark, that the luminous appearances of electrical action 
must be considered as secondary, while the uniform exertions of 
attractions and repulsions, under all circumstances, point them 
out as primary and invariable phenomena of electricity. This 
valuable communication is then. concluded by the important 
statement, that recently distilled mercury which has been after- 
wards boiled and cooled in the atmosphere, and which presents a 
perfectly smooth surface in a barometer tube, emits air when 
strongly heated in vacuo; and an instance is given in which the 
metal was observed to imbibe air. 
1X. Croonian Lecture—On the Anatomical Structure of the 
Eye; illustrated by Microscopical Drawings, executed by 
I’. Bauer, Esq. By Sir Everard Home, Bart. VPRS. 
The contents of this lecture would be unintelligible without 
the engravings, in which the structure of the visual organ is 
minutely and beautifully delineated. 
X. A Letter from John Pond, Esq. Astronomer Royal, to Sir 
H, Davy, Bart, PRS. relative io a Derangement in the Mural 
Circle at the Royal Observatory. 
As the amount of error occasioned by this derangement has 
been stated by Mr. Pond in the Preface to the Greenwich 
Observations for 1820; and as the derangement itself has been 
rectified by Mr. Troughton, itis unnecessary to abridge this letter. 
XI. On the Hinite Latent of the Atmosphere. By Dr. Wol- 
laston, VPRS. 
