420 Dr. Tyndall on the Reduction of Temperatures 



experiment of Peltier on the absorption of heat at a bismuth 

 and antimony joint. This has dra\\Ti from Mr. Adie a brief 

 communication, published in your Number for September, from 

 which it appears that the Avi-iter has never been able to obtain 

 Peltier's result ; he vii'tually denies its existence, and aifii'ms the 

 true state of the case to be that less heat is developed at some 

 junctions than at others, but that cold is never generated. An 

 objection precisely similar to that now urged by Mr. Adie in- 

 duced Lenz to repeat the experiment fifteen years ago*. To the 

 experiment of Lenz I took the liberty of drawing INIr. Adie's 

 attention in your October Number; 1 did so because Mr. Adie 

 had never mentioned it in his remarks, and it seemed to me to 

 offer a proof of the absorption of heat so ob\dous as to be imme- 

 diately appreciated. It does not however appear so to Mr Adie, 

 for in your last Number I find that he suggests a hygrometric 

 action as the probable cause of the diminution of temperatui'c 

 observed by L^nz. I should ill occupy your space were I to 

 dwell upon conjectures where the ' law and testimony ' of experi- 

 ment are so near at hand, and fact so readily attainable. If the 

 following results do not convince Mr. Adie, they will perhaps be 

 the means of clearing away whatever doubt his remarks may 

 have created in the minds of others. 



Experiment No. 1. — In Plate IV. fig. 1, A is a bar of anti- 

 mony, B a bar of bismuth, both bars being brought into close 

 contact at J. To the free ends of the bars the wires w w' are 

 soldered, and dip into the little pools of mercury m 7n' ; c is a 

 piece of cork through which the wires pass, and by taking which 

 in the fingers the wires w lo' may be easily moved from the pools 

 mm' to m m",the warming of the wires being prevented bythe cork. 

 From m m" wires proceed to a galvanometer, G, whose needles 

 prove themselves to be perfectly astatic by setting at right angles 

 to the magnetic meridianf. B is a single cell of Bunsen, from 

 which, when matters stand as in the figure, a current can be 

 sent through the bismuth and antimony pair. 



The voltaic circuit having been established, the curi'ent — a 

 very feeble one — was permitted to circulate for two minutes, its 

 direction being from antimony to bismuth across the junction ; 

 at the end of the time specified the wires iv w' were moved from 

 m m' to m m", a thermo-circuit being thus formed in which the 

 galvanometer was included ; the index of the instrument was at 

 once deflected, and the extreme limit of its first impulsion was 

 noted ; it amounted to 



75°. 



* Poggendorif's Annalen, vol. xliv. p. 342. 



t For an explanation of this, see an abstract of Dti Bois Reymond*s 

 Researches on .iVnimal Electricity, edited by Dr. Bence Jones. 



