418 
Proceedings of the Royal Society 
sion led to a very novel idea regarding the properties of matter, 
and, I may say, a novel discovery of action in connection with 
heat and electricity. To this action the name of the electric 
convection of heat has been given. When this is taken into 
account in connection with the discoveries of Peltier, Gumming, 
and Seebeck, it appears that the heat supply by which an engine 
driven by the thermo-electric current gets its energy may be not 
in a junction between two dissimilar metals, but by the peculiar 
absorption of heat, or generation of heat, which the discovery I 
have last mentioned points at when a current passes from hot to 
cold or cold to hot in the same metal. I am afraid the subject 
is somewhat involved ; but I can only say that if the Fellows of 
the Royal Society diligently read their own Transactions, it would 
not be necessary for me to speak about it, because it was very 
minutely unfolded in a paper published a good many years ago. 
I chanced to be the author of that paper myself, and I speak just 
now, I must confess, with a considerable pride of the position 
it bears in relation to Professor Tait’s discovery. This dis- 
covery is, that there are in many cases no doubt, but notably in 
cases in which iron is one of the metals, not merely one neutral 
point, as discovered by Cumming, but several neutral points. 
Tait finds that when a circuit, composed of iron and (let us 
suppose) platinum, has the temperature of one junction gra- 
dually elevated, while that of the other is maintained constant, 
the current first increases, then diminishes, then increases, then 
diminishes, — or, it may be, first increases, then diminishes to 
nothing, and goes in the contrary direction, attains a maximum in 
that contrary direction, then diminishes from that maximum to 
zero, and increases in the first direction to a maximum, and so on 
with every alternation. “ Multiple neutral points” is the shortest 
name I can give in words to the great discovery in Professor Tait’s 
paper. But I would do Professor Tait great injustice, and give you 
a very imperfect idea of the substantial character of the investiga- 
tion for which the award has been made, were I to lead you to 
suppose that it was merely a discovery which some of you might 
for a moment imagine could be hit off by chance, and by an ex- 
perimenter who had not his eyes absolutely closed. This discovery 
was made in the course of an elaborate investigation, of which 
