138 PROFESSOR TAIT ON A FIRST APPROXIMATION 
Nature [May 29th and June 12th], and to this I refer the reader for some 
speculations as to the connection of these phenomena with known chemical and 
magnetic relations, as well as for a great deal of additional matter connected 
with Thermo-electricity, but not so directly connected with my present sub- 
ject, the construction of a Thermo-electric Diagram. 
I have given this résumé of a few of my former papers to show how I was 
led to attempt the construction of a thermo-electric diagram, by the result of 
experiments originally devised to test the truth of a hypothetical application 
of the Dissipation of Energy. 
The following results were obtained mainly during the summer of the present 
year, the experiments being in great part made by Messrs Grete and C. G. 
Kwotr in my laboratory. The extracts above show sufficiently the nature of 
the processes employed, so that but a very few remarks need be made about 
the thermo-electric diagram (Plate VII.), which is constructed from them, and 
embraces the greater part of the temperature-region in which mercury ther- 
mometers can be used. Metals like bismuth and antimony are quite beyond 
the capabilities of even a double plate on this scale. 
1. A very small amount of impurity, or even of permanent strain, is capable 
of considerably altering the line of a metal in the diagram; so that I have given 
in general a sort of average position to each line, and have not attempted abso- 
lute exactness where it was obviously not requisite nor even desirable. N is the 
alloy of 15 Ir, 85 Pt described in the last extract above, M is the other alloy. 
Nos. 1, 2, 3 denote platinum-iridium alloys containing respectively 5, 10, 15 per 
cent. of the latter metal. These were prepared for me from pure metals by 
Messrs JOHNSON and Marruey, as | fancied from the behaviour of M and N that 
I might get a series of alloys whose lines should be parallel to that of lead. The 
result does not for the present appear encouraging. 
2. I have not yet been able to arrive at any definite conclusion with regard 
to the form of the dotted portions in the lines of nickel and of Gerraan silver. 
In fact, had it not been that the palladium line intersects that of nickel near 
the middle of the most mteresting region, I might have missed altogether the 
detection of the peculiarities of nickel, though I was led to seek for them near 
that region by induction from those of iron. It is obvious, in fact, from the 
diagram, that had copper, gold, iron, &c., been associated with nickel, the 
modification due to these peculiarities would have been only a very small 
fraction of the whole electro-motive force, and might easily have been attri- 
buted to errors of observation. As it is, my best specimen of pure nickel has 
been destroyed by exposure several times to a white heat, and I must wait for 
another before I can resume this part of the inquiry. 
3. Having made no direct experiments on the electric convection of heat in 
lead, I have retained its line as the axis, on the authority of Lz Rovx above 

