of Edinburgh, Session 1874-75. 
419 
results have been published from year to year, and generally within 
the two years for which the award has been given, in the Pro- 
ceedings of this Royal Society. From year to year Professor Tait 
had accurate measurements of thermo-electric currents executed in 
his laboratory. The results he tabulated and represented graphi- 
cally ; and even before making this discovery, he had made some 
exceedingly important contributions towards the laws of thermo- 
electric force in various combinations of metals. It was in pursu- 
ing this elaborate investigation that he came upon the very 
astounding discovery — I call it really astounding — that there are 
several consecutive neutral points between one and another of 
certain pairs of metals — iron, platinum, iridio-platinum. It is not 
my object to give you imperfectly a small part of the information 
contained in this paper of Tait’s. I desire rather to call your 
attention to a thing of much value which you have in your 
Transactions. But I may be allowed the pleasure of referring to 
the relation which my own previous investigation bears to this 
discovery of Tait’s. I did succeed in doing away with the Peltier 
effect at one junction ; I showed a thermo-electric current without 
the Peltier effect at one junction but with Peltier effect at the 
other junction, and the counter effect, absorption or evolution as it 
might be, made by my own thermo-electric convection in the 
homogeneous parts of the circuit. Now, Tait gives us a circuit in 
which there is no Peltier effect at all, and in which the whole 
origin of the power is to be found in absorption on the one hand 
and evolution on the other through electric convection of heat. I 
am afraid I have taxed your patience too long, because these 
matters have been reported in the Proceedings of the Society, and 
we have now a combined statement of the results in this paper. 
Before concluding, I wish to call your attention to the title 
of the paper, “ A Thermo-electric Diagram,” and the admirable 
manner in which Professor Tait has represented those results 
graphically to the eye, and the good use he has made of that 
graphical representation in aiding him to w r ork out rigorously the 
laws of the phenomenon. I am sure the Society will feel very 
great satisfaction in the award which has been made on the pre- 
sent occasion. (To Professor Tait) I have now much pleasure 
in presenting you with the Keith Medal. If it were necessary 
