120 The Rev. J. Bashforth on the Conducting Powers of Wires 



of the entire amount of water bein*?; indicated by the loss from 

 exposure to heat, childi'enite may be looked upon as consisting 

 of 8 atoms RO, 2 atoms alumina, 3 of phosphoric acid and 15 of 

 water, which constitution is represented by the formula — 



2(4RO, PO^) + 2 AlO^, POH 15H0. 



The first term in this formula is contained in triphyline, and 

 triplite is asserted to have a similar composition. The second 

 term, with a third part of the amount of water, is met with in 

 calaite. 



It is to the kindness of Mr. Brooke, M. Krantz, and Mr. 

 Lettsom that I am indebted for the materials on which I operated. 



XVI. Remarks on Mr. Dresser's Experiments on the Conducting 

 Powers of Wires for Voltaic Electricity, and on Mr. Joule's 

 Eaperiments with a powerful Electro-magnet. By the Rev. 

 J. Bashforth, Esq.^ 



IN the September Number of the Philosophical Magazine, 

 Mr. Dresser gave an account of some experiments with 

 respect to the conducting powers of wires, which appeared to 

 him to impugn the commonly received laws of their resistances 

 to the galvanic current. It is not rare to meet with objections 

 to well-established laws arising from a misapprehension of their 

 meaning, but objections of this kind are seldom founded on ex- 

 periments so good as these appear to be. ]\Ir. Dresser has not 

 explained how he compared the results of theory and experiment ; 

 but oit Table I. he observes, " .... it is evident that the often 

 quoted law of the conducting power of the wire being inversely 

 as the length does not obtain in short lengths. But there is an 

 evident intimation of some other law, and probably different for 

 different metals." Again, " Prom this Table (II.), compared 

 with Table I., it does not appear that with a thicker wire there 

 is any nearer approach to the old law, but also that some other 

 law obtains." On Table III. it is remarked, that " Increase of 

 intensity docs not appear to approach near to the supposed law." 

 And lastly, " This Table (IV.) does not coincide with the law of 

 conduction of wires of different diameters being as the squares 

 of the diameters." 



It seems to me that all these erroneous conclusions spring 

 from a wrong application of the laws quoted. The galvanic cur- 

 rent has other resistances to overcome besides that of the 1, 2, 



*' Cominuuicated by the Author. 



