RECENT PROGRESS IN PHYSICAL SCIENCE. 
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work, more perhaps than that of any other at this period, 
developed the idiosyncracies of mercurial thermometers 
and showed how their inherent errors were to be avoided 
and allowed for. It is impossible to fully discuss these 
questions here; suffice it to say that the gas thermometer 
in one form or another still remains the theoretical standard— 
that is to say, its scale of temperature is accepted as the 
closest approach we have to the ideal thermodynamic scale, 
in which equal intervals of temperature represent equal 
amounts of thermal energy. In spite of this admirable 
quality, however, every investigation with the air thermom¬ 
eter but adds to the mass of existing evidence to the effect 
that the instrument is subject to large accidental errors, and 
that its use is attended with serious difficulties. What is of 
much greater importance, recent progress in science has neces¬ 
sitated the measurement of temperatures beyond the practical 
limits of even the air thermometer. Modern experiments 
with liquified and solidified gases have opened up a field of 
observation down to the very verge of the absolute zero of 
temperature, while on the other hand students of the phe¬ 
nomena of fusion and volatilization of refractory substances 
desire to measure accurately the very highest temperatures 
we can produce. 
The response of the physicist to this demand for accurate 
measures of temperature over the entire range experienced 
has been partly met, at least, by a new instrument possess¬ 
ing many admirable qualities, namely, the platinum ther¬ 
mometer. Satisfying to a remarkable extent many of the 
requirements of a practical working standard, this instru¬ 
ment has been steadily gaining favor for a period of over 10 
years. 
The idea was first seriously proposed by Siemens and fol¬ 
lowed up by the construction of several pyrometers which 
were submitted to the British Association in 1874. These 
proved to be failures, however, seemingly due to ignorance 
and neglect of a few simple structural precautions that should 
have been observed. The idea was afterwards taken up by 
