1872.] Electricity. 405 
elearicity. The currentsdo not sensibly depend upon the heat produced by 
flexure. Flexures in contrary direGtions in the length of the wire produce 
currents in opposite directions. A diminution or augmentation in the rapidity 
of flexure produces a diminution or augmentation of the intensity of the 
electric current. A strip of different metals soldered together gives a current 
of less intensity than a strip of a single metal. 
It is interesting and not uninstructive to occasionally take retrospective 
views of progress in science, and to note the previsions of the more striking 
inventions. Whether Shakespeare when he made Puck say, “Tl draw a 
girdle round the earth in forty minutes,” had dreams of the then future 
eleGric telegraph, cannot be supposed; but we have more definite fore- 
shadowings in Strada’s ‘‘ Prolusiones Academice,” 1617, proposing a dial with 
alphabet and magnetic needle. Addison alludes to this invention in the 
“« Spectator,” No. 244, 1712. Glanvill, in his “‘ Vanity of Dogmatising,” 1662, 
says :—‘ To confer at the distance of the Indies by sympathetic conveyance 
may be as useful to future times as to us in a literary correspondence.” 
Evidently he is here thinking of the magnetic needle, for he continues after- 
wards to discourse of ‘“‘conference at a distance by impregnated needles.” 
Bailey’s ‘‘ Dictionary,” 1730, article “‘ Loadstone,” says :—‘‘ Some authors write 
that, by the help of the magnet or loadstone, persons may communicate their 
minds to a friend at a great distance; as suppose one to be at London and the 
other at Paris, if each of them have a circular alphabet, like the dial-plate of a 
clock, and a needle touched with one magnet, then at the same time that the 
needle at London was moved, that at Paris would move in like manner, 
provided each party had secret notes for dividing words, and the observation 
was made at a set hour, either of the day or of the night.” Sir Francis Ronalds, 
in 1816, constructed a tension telegraph at Hammersmith, the signals being 
read off pith balls. In 1816 also Andrew Crosse said :—‘‘I prophesy that 
by means of the electric agency we shall be enabled to communicate our 
thoughts instantaneously with the uttermost parts of the earth.” This 
remark, then a wild chimera, has been quickly achieved; not only can we com- 
municate with the most remote continent, but we could, undoubtedly, had we 
the wires laid, telegraph a signal eight times round the world in one second. 
In Pfliiger’s ‘* Archive,” Professor L. Hermann has described some experi- 
ments as to the condudtibility of living muscle. He finds that living muscle 
offers very much greater assistance to an electric current passing across the 
fibres than along them, in the ratio of 7:1. Muscles in the condition of rigor 
mortis do not show this difference. The specific resistance of living muscle in 
the longitudinal direction, taking the length of mercury as unity, 1s 2,330,000, 
and in transverse direction 15,134,000. A similar difference occurs in the case 
of the nerves, the ratio being then 5:1. The specific resistance of nerve in 
the longitudinal direction is 2,554,000, and in the transverse direction 12,586,000, 
the resistance of mercury being again taken equal to 1. The longitudinal 
resistance of nerve is augmented by heating it to 50° C. (122° F.), the trans- 
verse resistance simultaneously diminishing. Professor Hermann thinks 
these differences of the resistance of the longitudinal and transverse sections of 
muscle and nerve due to the different polarisation of the sheath and nucleus of 
the fibres, and elucidates this by mathematical formule. 
Professor J. T. Bottomley, M.A., F.C.S., describes the improved form of 
gravity battery, as devised by Sir William Thomson, and in use in the 
Physical Science Laboratory of Glasgow University, as follows:—The cell is 
of glass, a pan made by glass-blowers for containing milk. The diameter is 
21 inches. A disc of thin sheet copper is laid on the bottom; and a thick 
copper wire covered with gutta-percha is soldered to the copper disc, and rises 
to the top of the cell as an electrode. In the upper part of the cell is a heavy 
mass of zinc, cast into the form of a circular gridiron, with three ears or pro- 
jections, which rest on the edges of the glass. The gridiron shape is adopted 
in order to permit the hydrogen to escape. The distance between the zinc 
and copper plates is about 24 inches. A large sheet of parchment paper covers 
the under surface of the zinc, and the corners and edges of the paper are 
