55G 



On the Construction of Thermopiles. 



so that the light pair arrived rather more rapidly at the condition of equi- 

 librium than the heavier pair. 



Although the above experiments are far less complete than I could 

 have wished, they are sufficient to show that the sensibility of thermo- 

 piles may be considerably increased by diminution of the section of the 

 bars composing them ; whether they may be with advantage reduced to a 

 greater extent than I have already done I cannot say, but I am inclined 

 to think that they may. I have ascertained from Messrs. Elliott that the 

 alloys used by them in the construction of thermopiles, at the time when 

 I received mine from them, were 32 parts of bismuth + 1 part of anti- 

 mony, and 144- of bismuth +1 part of tin. If allowance be made for the 

 substitution of the first of these two alloys for pure bismuth, the differ- 

 ence between Elliott's pile and the pairs II. & III. will be rather greater. 

 The pile by Messrs. Elliott, if made of the same metals as I employed, 

 would have been reduced in power from 1 to 0'9. 



The construction of thermo-couples, on the plan I have described, is 

 comparatively easy. In about two hours I was able to make one, and in 

 more experienced hands their construction would be still easier. 



An experiment was made with one of the piles to ascertain whether, 

 when the heat was not directed centrally on the pile, much diminution of 

 power would take place. There ivas less deviation in consequence of the 

 increase of the mean distance which the heat had to travel before it 

 reached the soldering ; but I believe that this defect might be remedied, 

 probably without diminution of the power of the pile, by increasing the 

 thickness of the face, and leaving the dimensions of the bars the same. 



