108 
Ordinary Meeting-, March 8th, 1859. 
W. Fairbairn, F. R.S., &c.. President, in the Chair. 
A conversation having taken place respecting Sir W, 
Armstrong’s new gun, Mr. Roberts stated that he had, very 
many years ago, constructed a rifled cannon for the purpose of 
firing elongated shot coated with lead. Dr. Smith considered 
that the great merit of the new gun consisted in the manner 
in which the internal tube of steel was enveloped with 
wrought iron. The difficult problem of forming a perfect 
compound structure had received solution in the hands of 
Sir W. Armstrong, while others had failed. 
Dr. Joule read an extract from a letter he had some time ago 
received from Professor W. Thomson.— “ I havehadan apparatus 
for Atmospheric Electricity put up on the roof of my lecture 
room, and got a good trial of it yesterday, which proved most 
satisfactory. It consists of a hollow conductor supported by 
a glass rod attached to its own roof, with an internal atmo- 
sphere kept dry by sulphuric acid : the lower end of the glass 
rod is attached to the top of an iron bar, by which the hollow 
conductor is held about two feet above the inclined roof of the 
building. A can, open at the top, slides up and down on the 
iron bar which passes through a hole in the centre of its 
bottom, and, being supported by a tube with pulleys, &c. 
below, can easily be raised or lowered at pleasure. A wire 
attached to the insulated conductor passes through a wide 
hole in the bottom of the can, and is held by a suitable 
insulated support inside the building, so that it may be led 
away to an electrometer below. To make an observation, the 
wire is connected with the earth, while the can is up, and 
envelopes the conductor — its position when the instrument is 
Pecceedikgs — Lit. & Phil. Society— No. 12 . — Session, 1868 - 9 . 
