SOif Mr. Watkins on Thermo-electricity. 



In instituting a comparison between the geometrical and 

 analytical methods, in any given instance, account should of 

 course be taken of the amount of extraneous aid required for 

 the furtherance of each process. In analysis the truth is in 

 general evolved from the fundamental conditions, independ- 

 ently of subsidiary propositions beyond those which consti- 

 tute the first principles of the subject. In geometry, on the 

 contrary, we cannot arrive at the same conclusion without the 

 assistance of some neighbouring truth or chain of truths nearly 

 as remote from first principles as that to be established. It 

 may be proper to remark, that the expression — 2m cos /3, 

 for the ordinate of the focus, is deduced from the simplest 

 and most obvious considerations. The abscissa of the focus is 

 m, which is also the radius vector of the origin ; the ordinate 

 is thus the base of an isosceles triangle whose side is m, and 

 angle at the base /3 or the supplement of /3, accordingly as this 

 ordinate is negative or positive; its true value is therefore 

 that employed above. 



Aug. 7, 1837. 



XXXVII. On Thermo-electricity. By Mr. Francis 

 Watkins. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 HPHAT species of electricity developed by the influence of 

 -"■ temperature first observed and made known to us by M. 

 Seebeck, in communications to the Academy of Berlin, in the 

 years 1821 and 1822, having latterly attracted increased at- 

 tention in this country, through the very interesting letter of 

 Professor Wheatstone, published in your last May number, 

 page 4? 15, and also from a valuable communication of Professor 

 Andrews, printed in the following June number, page 433, I 

 venture to trouble you with a few remarks, which I flatter 

 myself if admitted into your miscellany will not prove unac- 

 ceptable to many of your readers. 



Professor Wheatstone's communication informs us that 

 Cav. Antinori obtained the spark from a thermo-electric pile 

 of Nobili's construction, consisting of twenty-five elements, by 

 employing an electro-dynamic helix and a temporary magnet, 

 while Professor Wheatstone employed a thermo-electric pile 

 of thirty-three elements of bismuth and antimony, formed 

 into a cylindrical bundle f of an inch in diameter and 1^- in 

 length : the poles of this pile were connected by means of two 

 thick wires, with a spiral of copper ribbon fifty feet in length 



