26 >) REPORT—1858,..--- , 
On Induced Electrical Discharges taken in Aqueous Vapour. 
By J. P. Gassiot, V.P.R.S. 
If the tube of a well-constructed water-hammer is partly covered with two sepa- 
rate coatings of tinfoil, and the coatings are connected, one with the outer, and the 
other with the inner terminal of an induction coil, a discharge will be observable 
through the centre of the tube in the form of a wave line. On repeating this expe- 
riment, I ascertained that the vacuum in the tube was very much deteriorated. I 
could no longer produce that peculiar bubbling in the ball! of the apparatus which is 
always attainable by gently heating the tube with the warmth of the hand; this 
bubbling was originally very sensibly perceptible in the tube I now exhibit when I 
first received it from the maker, Mr. Casella. I have repeated the experiment with 
other water-hammers, and always with the same result; but I have not yet opened 
one to examine whether the vapour has been decomposed, and gas evolved. 
“ At the close of the reading of the paper, the room was darkened, and Mr, Gassiot, 
assisted by Mr. Ladd, exhibited the experiment. 
On the Phosphorescent Appearance of Electrical Discharges in a Vacuum 
made in Flint and Potash Glass. By J. P. Gasstot, V.P.R.S. 
The discharge from an induction coil, when taken in a vacuum tube made of flint- 
glass, has (under certain conditions) the property of rendering the glass highly phos- 
phorescent, the phosphorescence being denoted by the intense blue colour of the 
glass with which the stratifications are surrounded. On trying the discharge in some 
vacuum tubes I had obtained from M. Geissler, of Bonn, I observed that the phos- 
phorescence was no longer blue, but was of a slight green colour. To test whether 
this difference was due to the gaseous matter remaining in Geissler’s tubes, or to the 
character of the glass which he uses, I had Torricellian vacuums prepared in German 
glass tubes, and in this manner ascertained that the difference in the colour was 
entirely due to the character of the glass: that of Germany is, I believe, made with 
potash, and is entirely free from any lead, while in the English flint-glass lead is in- 
troduced to some extent. I have recently obtained a vacuum tube from Bonn, which 
shows this difference in a very beautiful manner : the outer ends of the tube are com- 
posed of German glass, the centre of the tube is of English glass; by this arrange- 
ment the contrast between the two is very manifest. 
Exhibition af Apparatus showing the Correlation of Forces, and Exhibition 
of Heating Effects, by Mechanical Operations, on a peculiar Form of 
Antimony. By GrorcE Gore. 
On an Improved Induction Coil. By W. Lapp, Chancery Lane. 
Having been rather extensively engaged for the last two years in the manufacture 
of induction coils, and having received the constant and able advice of Mr. J. P. Gas- 
siot, and the practical suggestions of Mr. C. A. Bentley, I have thought that a brief 
description of the machine as it is now made, with the results obtained, may not be 
uninteresting. My object has been not to make very large machines, but to obtain 
the greatest results from a three-mile coil, that being sufficiently large for all ordi- 
nary purposes. I find the best length for the iron core to be 13 inches and about 
15°8 diameter, composed of fine iron wire not larger than No. 22, very carefully 
annealed. The primary wire should be of sufficient size to carry freely the whole of 
the battery current, and of sufficient quantity to saturate thoroughly the iron core. 
with magnetism. For this purpose I use three layers of one continuous No. 12) 
copper wire carefully annealed: if more layers.are used, I find that the secondary 
wire is removed too far from the magnetic influence. The secondary wire ought not 
to be larger than No. 35, covered with silk, which must be laid on perfectly even 
and insulated from the primary wire, and also from the layers of the secondary next 
ta it. I find the best insulating medium to be the thinnest gutta percha made, and 
which I believe to be the only gutta percha sold which cannot be adulterated ; it is 
