VOL. LXin.3 PHILOSOPHICAL TRANSACTIONS. 469 



found to be the 3 following: 1st. The settling of a fixed point, from which 

 every measure of the same kind should be taken ; such, for instance, as that of 

 boiling water in a thermometer, when the barometer is at a certain height. 2d. 

 Degrees equally determined, or comparable, in different hygrometers, such as 

 are in the thermometer, the scales of Fahrenheit, Delisle, Reaumur, &c. 3d. 

 Constancy in the variations produced by the same differences of humidity. 



The result of Mr. D.'s elaborate researches on this subject, was, the adopting 

 for an hygrometer a small tube of ivory, inclosing a portion of quicksilver, which 

 was made to rise and fall in the tube, like a thermometer, by the contracting or 

 widening of the tube, in consequence of more or less moisture in the surround- 

 ing medium. 



XX XIX. On the Electric Property of the Torpedo.* In a Letter from John 

 Walsh, Esg.,f F. B. S., to B. Franklin, Esq., LL. D., F. R. S., &c. p. 461. 

 Letter from Mr. IValsh to Dr. Franklin, dated la Rochelle, [2th July, 1772. 

 — " II is with particular satisfaction I make to you my first communication, 

 that the effect of the torpedo appears to be absolutely electrical ; by forming its 

 circuit through the same conductors with electricity, for instance, metals and 

 water; and by being interceptetl by the same non-conductors, for instance, glass 

 and sealing-wax. I will not at present trouble you with the detail of our experi- 

 ments, especially as we are daily advancing in them ; but only observe, that we 

 have discovered the back and breast of the animal to be in different states of 

 electricity ; I mean in particular the upper and lower surfaces of those 2 assem- 

 blages of pliant cylinders, of which you have seen engravings in Lorenzini.t 

 By the knowledge of this circumstance we have been able to direct his shocks, 

 though they were very small, through a circuit of 4 persons, all feeling them; 

 likewise through a considerable length of wire held by 2 insulated persons, one 

 touching his lower surface, and the other his upper. When the wire was ex- 

 changed for glass, or sealing- wax, no effect could be obtained : but as soon as it 

 was resumed, the 2 persons became liable to the shock. These experiments 

 have been varied many ways, and repeated times without number, and they all 

 determined the choice of conductors to be the same in the torpedo as in the 

 Leyden phial. The sensations likewise, occasioned by the one and the other in 

 the human frame, are precisely similar. Not only the shock, but the numbing 

 sensation which the animal sometimes dispenses, expressed in French by the 

 words engourdissement and fourmillement, may be exactly imitated with the 



• Raja Torpedo, Linn. 



+ For this ingenious paper the author was presented with the Copleian medal. 

 J Osservazioni intornoalle torpedini di Stef. Lorenzini 1678. Redi appears to be the first who re- 

 maiked these singular parts of the torpedo in l666". Franc. Redi, Exper. Nat. — Orig. 



