On a Simple Method of Constructing high Electrical Resistance. 41 



the terms of the problem submitted to us — for example, on the 

 assumption that one of the partial differential coefficients p } q> r } 

 s, t vanishes. 



6 New Square, Lincoln's Inn, 

 June 20, 1870. 



VI. On a Simple Method of Constructing high Electrical Re- 

 sistance. By Samuel E. Phillips,, Jun.* 



AT present resistance-coils are mostly made with German- 

 silver wire ; and a set of coils equalling 10,000 B.A. units 

 forms a box of convenient size. But in electrical research resist- 

 ances of several million units are often useful ; and to produce 

 such with wire in the ordinary way would be both expensive and 

 cumbrous. 



Latterly Mr. Hockin has used selenium for this purpose. Fine 

 glass tubes with a platinum wire blown in at each end and filled 

 with different fluids, according to the resistance required, have 

 also been largely used; but these latter necessarily give very 

 variable results, owing to polarization and electrolysis ; and the 

 former, I believe, are somewhat difficult to construct. 



Requiring a high resistance for some experiments, I made one 

 as follows : — Upon a strip of vulcanite, 6 inches long by 1 inch 

 wide, I ruled several pencil lines with an ordinary H.B. pencil in 

 such a manner as to produce a continuous line about ^ of 

 an inch wide and 4 inches long. At the extremities of the line 

 I rubbed the pencil plentifully over a space as large as a six- 

 penny piece, upon which I firmly screwed two binding-screws 

 by means of "nuts" underneath, and, gently dusting off all su- 

 perfluous plumbago, varnished the whole with several coats of 

 pure shellac varnish. 



The above arrangement gave me a resistance of slightly over 

 two million B.A. units. It was constructed three months ago, 

 and up to the present time the resistance has remained very con- 

 stant. I have tested it repeatedly with 100, 200, and 300 cells, 

 and have always obtained the same result within very small 

 limits. It is also beautifully steady with prolonged battery 

 contact. 



Mr. G. Preece has kindly tested a resistance made in the 

 above manner for me, and finds it very constant, only getting an 

 alteration of about 0-5 per cent, for 5° F. I have mounted a 

 vulcanite slab with twenty binding-screws, giving a wide range 

 of varied resistances by combination or otherwise, and hope 

 shortly to make some experiments with the view of determining 

 the ratio of its alteration by difference of temperature. 

 * Communicated by the Author. 



