244 Mr. Tatiim on Electro-Magfietism. 



helix to be magnetized, their jioles will be in an ojjposite di- 

 rection to what would have been produced by a right-handed 

 one. 



I think this contrary spiracular circulation of the fluid, when 

 proceeding from ojjposite poles of a Voltaic appai'atus, will 

 account for the attraction of parallel wires when proceeding 

 from Voltaic poles similarUj situated ; but repelled when pro- 

 ceeding from poles (Jissimilarhj situated, for then the circula- 

 tion of the fluids round the wires will be opposite to each other, 

 and of course will repel. This may be illustrated by placing 

 a left- and right-handed helix parallel to each other; for so si- 

 tuated, the dii-ection of these coils will be seen to be opposite 

 to each other ; which will represent the course of the fluid 

 round parallel wires proceeding from poles oppositely situated. 



The apparatus which I made use of to produce the effects 

 on the needle consists of a copper vessel A B C D, fig. 12, 

 two feet deeji, upwards of twenty-two inches broad, and nearly 

 two inches and a half wide, in which is placed a plate of 

 zinc E F, tv/ en ty- three inches deep, and full twenty inches 

 broad, wdth a wire L jiroceeding from the zinc, and another 

 wire K attached to the copper, on which I can slip horizontal, 

 perpendicular, and helix wires. The vessel holds about six gal- 

 lons of diluted acid, which added to the weight of the zinc 

 plate (a quarter of a cwt.) renders it too heavy to decant the 

 fluid. It is therefore provided with a cock, by which the diluted 

 acid can be drawn ott' without any labour. When this apparatus 

 was fresh charged with nitro-sulphuric acid twelve times di- 

 luted, its magnetic properties were so powerful, that it in- 

 fluenced a large heavy needle about two feet distant ; it also 

 rendered pieces of steel magnetic, which were placed in a helix 

 sufficiently strong to lift each other, before the vessel could be 

 quite filled with the diluted acid, although it was poured as 

 (juick as possible from a four-gallon carboy. Its attracting 

 and repelling properties were much too strong to make the 

 above ex|ieriments, until the acid had remained in the ap- 

 paratus some time, by which its power was i-educed. This ap- 

 paratus, when in full action, is admirably calculated to show 

 the dissimilar effects of right- and left-handed helixes on pieces 

 of steel to be magnetized. 



I am yours, &c. 

 Dorset-street, April 1>, 18'2;{. J. Tatum. 



About a week ago I sent you a paper on Electro-magnetism, 

 in which I noticed, that the magnetic fluid circulated round 

 the north end of a magnet in a different direction to what it 

 did round the south end. Thi^ opinion was in consequence 



of 



