THE 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



30"' NOVEMBER 1823. 



LXVI. An Accoimt of some Electro-magnetic CovibinationSi 

 for exhibiting Thermo-electric Phcenomena, invented hy Mr. 

 James Maksh* of Woolwich: with Experiments on the same. 

 By Peter Barlow, Esq. F.R.S., of the Royal Military Aca- 

 demy, Honoraiy Member of the Camhridge Philosophical So- 

 ciety and of the Society of Civil Engi?ieersf. 



pROFESSOR GUMMING having very obligingly fa- 

 •*- voured me with a copy of his highly interesting paper 

 printed in the Transactions of the Philosophical Society of 

 Cambridge, for the present year, ' On thermo-electric Phaeno- 

 mena,' I put it into the hands Mr. Marsh, requesting him to 

 copy any of the apparatus he there might find described, 

 with a view to repeating such of the experiments as were re- 

 ported. This he very readily undertook, and soon brought 

 me not only those 1 had requested him to copy, but several 

 new ones, which latter it is my intention to describe in this 

 paper. The most essential apparatus in these experiments is 

 a very sensible galvanometer. Professor Gumming, who was 

 the first to employ this useful machine J, has not very distinctly 

 stated his construction of it. I cannot tell, therefore, how nearly 

 that I am about to describe may resemble his ; at all events 

 Mr. Marsh's galvanometer is a very simple and sensible in- 

 strument, and its construction will not be uninteresting to 

 some of your readers. 



AB, GD, (PL V.) fig. 1, are two wooden supports or pil- 

 lars, through which pass brass wires, having each at its ex- 

 tremity a small brass cup ; to the other extremity of each is 

 attached by good contact the square helix cage shown in the 

 figure : on the top of the prop E, is a fine point carrying a 

 very light and delicate compass needle with a card below; FG 

 is a stand for holding the bar R S, of bismuth, antimony, or 

 other metal; and n7u ?i'?w', are wires of a different metal sol- 

 dered or bound round at the ends R and S. The set screw 

 at s is for adjusting to any height. The brass cups being now 



* We are glad to find that this ingenious self-taught artist has com- 

 menced the business of chemical and philosophical instrument-maker in 

 Woolwich — Kdit. 



+ Communicated by the Author. 



X Sec Tran». Camb. Phil. Society for 1S21. 

 Vol. 02. No. 307. A'oT'. 1823. " Ss rubbed 



