23 
Ordinary Meeting, December 11th, 1860. 
Dr. J. P. Joule, President, in the Chair. 
Dr. Fairbairn brought before the meeting four specimens 
of Submarine Telegraphic Cable, as constructed by Messrs. 
Hall and Wells. This cable has a copper wire insulated by 
india rubber in the centre for the transmission of the electric 
current. Outside of this are twenty longitudinal strands of 
hemp steeped in pitch and cork dust, and eight steel wires 
braided together with twenty-four strands of hemp saturated 
with Stockholm tar. The specific gravity of the cable in sea 
water is 1.4 and its weight in air 0.82 ton per mile. 
The length that would break with its own weight when sus- 
pended in sea w'ater is 10,810 fathoms; its tensile strength 
being 2.875 tons. Dr. Fairbairn presented an account of 
experiments which had been made on the elongation of a 
sample of the cable twenty feet long by the application of 
different tensile forces. With a force of 4,480 lbs. there was 
an elongation of half-an-inch, and after the weight had been 
removed the cable was found to be permanently stretched 
■vVths of an inch. With a force of 6,440 lbs. the cable broke 
after having stretched 1^ 0 - inches. 
Professor Roscoe explained the recent discoveries by 
Bunsen and Kirchoff of the lines in the spectrum produced by 
various substances when ignited in the flame of a laboratory 
lamp. He exhibited beautiful chromo-lithographic drawings 
of the spectra produced by lithia and various other earths 
and alkalis. Lithia, which had formerly been supposed to be 
a very rare earth, was by this means proved to be one of those 
most extensively distributed. Professor Roscoe stated that 
Bunsen had, by this new and most delicate system of analysis, 
been led to the discovery of a new metal which was present 
in a mineral spring in so small a quantity that twenty tons 
had to be boiled down to obtain 250 grains of the metal. 
Prockethngs — Lit. & Phil. Society — N o. !>. — Session', 1S60-G1, 
