212 Mr. Curtis' s Descriptions of some hitherto nondescript 



ing, viz. That the conducting power of wires of the same 

 metal varies as the squares of their diameters directly, and as 

 their lengths inversely. " Or we may say, that the intensity 

 or conducting power varies as the mass or weight directly, and 

 the square of the length inversely." The law thus obtained 

 for magneto-electricity is exactly the same as that obtained by 

 M. Becquerel for voltaic electricity. 



I have formerly shown that this law of M. Becquerel does 

 not give even an approximation to the truth for voltaic elec- 

 tricity*, and as all are agreed about the identity of the electri- 

 city from these two sources, the law thus obtained for mag- 

 neto-electricity must be equally remote from the truth. 



I have proved, also, that had the conducting power of liquid 

 conductors varied inversely as their lengths, the voltaic bat- 

 tery could not have existed f . In like manner it may easily 

 be shown that had the conducting powers of wires varied in- 

 versely as their lengths, the multiplier, or galvanometer, could 

 have had no existence. For suppose a galvanometer coil be 

 made with a wire 10 feet long, having 10 folds, and another 

 similar coil made with a wire 40 feet long, having 40 folds, 

 the latter coil would, on that supposition, be exactly equal to 

 the former. If the conducting power vary nearly as the squai'e 

 root of the length, the power of the second would be double 

 that of the former, which will be found by experiment not far 

 from the truth. 



The very existence, then, of the multiplier, as an accumidator 

 of feeble voltaic electricity, is a glaring proof of the fallacy of 

 the conclusion, that the conducting power varies inversely as 

 the length. 



I shall not enter on the examination of the third part of the 

 Bakerian Lecture ; for since the method employed has been 

 insufficient for detecting the laws of conduction in the same 

 metal, it is equally inapplicable to determine the ratio of the 

 conducting powers of different metals. 



XXXVII. Descriptions of some hitherto nondescript British 

 Species of May-fies of Anglers. By J. Cu rti s, Esq., /*'. L.S.,fyc. 

 [Concluded from page 125.] 

 Gen. 750. Phryganea Linn. 



6. minor Curt. 

 11 lines: brown, antennae annulated ; superior wings variegated with nu- 

 merous ochreous dots, forming two large spaces on the costa, two abbre- 



• See Phil. Trans. 1833, Part IF. p. 313— 316; or Lond. and Edinb. 

 Phil. Mag. vol. iii. pp. 145, 146. — Edit. 



| Philosophical Transactions for 1832, Part II. p. 289. 



