Natural Philosophy. — Electricity. 165 
Having reduced the power of a dipping needle nearly 8 times, 
by two magnets placed in the line of the dip, Mr Barlow ob- 
served, that it passed suddenly from one half-quarter degree to 
another, more or less, so as to give a difference in the dip of 1 
in one day. It seldom, however, shewed any tendency to re- 
turn, though, when vibrated at night, it commonly took up its 
morning position. The same sort of daily motion appeared 
whether the face of the instrument was to the E., W., N., or S. . 
Mr Barlow is of opinion, that the solar light, and not the solar 
heat, is the principal operative agent in producing the daily va- 
riation. 
ELECTHICITY. 
10. Electricity produced by separation of parts. — In the 
fine water-proof cloths manufactured by Charles Macintosh, Esq. 
of Glasgow, where two pieces are cemented together by caout- 
chouc, dissolved in coal-tar oil, the adhesion is so complete, that 
when the two are torn from one another in the dark, there is a 
bright flash of electric light, similar to what is produced by tear- 
ing asunder plates of mica, by bursting Prince Rupert’s drops, 
or by breaking barley sugar, or sugar candy. Upon trying this 
experiment with different substances, we found that flashes of 
light were distinctly produced, by tearing quickly a piece of cot- 
ton cloth. 
11. Prof. Cumming's Table of Thermo-Electrics. — In the 
following table of thermo-electrics, by Professor Gumming, each 
substance is positive to all below, and negative to all above it, two 
being used together. 
Cobalt, Brass, Charcoal, 
Silver, Copper, Plumbago, 
Tin, Gold, Iron, 
Lead, Zinc. Arsenic, 
Rhodium. Antimony. 
Annals of Phil. vol. vi. p. 170, N. S. 
Bismuth, 
Mercury, \ 
l^ickel, f 
Platina, 
Palladium. 
lie, } 
ELECTEO-MAGNETISM. 
12. Neiv Phenomenon in Electro-Magnetism. — Sir H. Davy 
found, that when two wires were placed in a basin of mercury, 
perpendicular to the surface, and in the voltaic circuit of a bat- 
tery, with large plates, and the pole of a powerful magnet held 
