306 Mr. Watkins on Thermo-electricity. 



in which metals like antimony ^and bismuth joined together by 

 soft solder form a part. I arrange one of my extremities of 

 the pile of strong sheet copper, cut like a comb, and covered 

 with soft solder (the latter is a plan, I believe first suggested 

 by Dr. Hare, to obviate the trouble of amalgamating at every 

 experiment), and when the moveable extremity of my Henry's 

 coil is passed over the comb, and the thermo-electric pile in 

 action, splendid sparks are seen every time the moving part 

 of the coil breaks the circuit by leaving a tooth of the comb. 

 I have used stellar-formed wheels, vibrating pendulums, &c, 

 &c, to break contact, and all give beautiful sparks and shocks 

 when desired. When a small steel file forms the moving 

 part, splendid scintillations are noticed, and to do away with 

 amalgamation, soft solder, &c, 1 frequently employ an old 

 plan of silver against silver for making and breaking contact; 

 the spark thus developed is vivid, and, as we might expect, of 

 a beautiful green hue; but it must be confessed that no sparks 

 are so brilliant as those from the surface of mercury, for we 

 can seldom obtain other metallic surfaces equally clean. 



I desire here to record what I believe to be novel, that on 

 the 27th of last June, with a thermo-electric pile, consisting 

 of thirty pairs of bismuth and antimony, 1^ in. square and \ 

 thick r with the radiation of red hot iron at one extremity and 

 ice at the other extremity, a soft iron electro- magnet, under 

 the inductive influence of the electricity thus generated, sup- 

 ported ninety-eight pounds weight, the most powerful thermo- 

 electric magnet I have heard of; but it must be observed that 

 this is no maximum, for whoever employs a larger elementary 

 battery will no doubt obtain greater effects, not only as re- 

 gards inductive influence on soft iron, but all others in which 

 the influence of temperature may be exerted. 



There is an ample field for investigation open for those 

 who have leisure on this subject. Who knows but hereafter 

 electro-magnetism may be employed as a prime mover, and 

 that a thermo-pile may be the exciting cause? 



By adopting Professor Henry's method of giving the shock 

 with his flat ribbon coil, from a single pair of voltaic plates, I 

 have succeeded in obtaining in a marked and decided manner 

 the physiological effects on the tongue, with the thermo-pile 

 of thirty pairs of elements. 



The spaces in your excellent journal are far too valuable to 

 be occupied by lengthened descriptions of the various-formed 

 metallic elements that I have used and that may be employed, 

 and even of those that I have found best suited for the experi- 

 mental inquirer and public demonstrator. Nor dare I venture 

 to occupy your pages with long details of the results arrived 



