ANNIVERSARY ADDRESS. 23 
news to those who still think that rock oil is of organic origin, 
and therefore not likely to exist in unlimited quantities. 
A good deal of work has been done recently in improving our 
means of measuring temperatures. Many people think that as 
temperature measurements have been made for so many years 
they must necessarily have been carried to a high point of accuracy. 
In special cases such as the experiments of Regnault this is no 
doubt true, but the temperatures investigated did not lie much 
outside the ordinary range—i.e. up to 300° Centigrade—and the 
apparatus was quite unmanageable under ordinary conditions of 
work. Improvements have been made in two ways. The electrical 
resistance of platinum has been accurately determined as a fune- 
tion of the temperature, and it has been shown that different 
samples of commercially pure wire behave similarly. Platinum 
wire resistance thermometers are now articles of commerce. The 
thermoelectric couple has also been investigated by Le Chaletier 
for hizh temperatures, and a junction of platinum and a ten per 
cent. alloy of rhodium and platinum has been made to yield reliable 
results. On the other hand a most extraordinary improvement in 
the detail of correcting ordinary thermometers has been achieved 
by M. Guillaume of the Bureau International des Poids et Mésures: 
with the result that thermometers can now be made by a skilful 
Parisian maker, which after passing through the hands of M. 
Guillaume’s assistants, will give correct readings on an actual 
scale of temperature to within one two-hundredth of a degree 
centigrade. I have such instruments in my possession. 
The crowning discovery of the year however, has been that of 
& new component of the atmosphere by Lord Rayleigh. This gas 
ey virtually discovered some two years ago and has now been 
isolated by Lord Rayleigh and Prof. Ramsay. About 1885 Lord 
Rayleigh began to redetermine the density of gases with a view 
to testing Prout’s hypothesis, As a result there is now no doubt 
that the ratios of the atomic weights of oxygen and hydrogen do- 
hot accord with the hypothesis in question ; a result which had 
been provisionally established by Stas for other substances. 
