342 
Deville and Troost were made, with a geo- 
logic aim in view, in the laboratory of the 
U.S. Geological Survey. Finally, porcelain 
air thermometry was taken up with great 
vigor by the Reichsanstalt. These results, 
due to Holborn and Wien, are now almost 
exclusively quoted and carry the stamp of 
the great institution from which they ema- 
nated. They have been wisely made com- 
mercially available by the deposition, with 
Heraus, in Hanau (Germany ), ofa platinum 
rhodium alloy definitely calibrated for a 
temperature range of 1400°. 
Apart from this, these researches contain 
no essential novelty, except, perhaps, a more 
detailed attempt to investigate the stem 
error of the thermometer bulb; their pro- 
cedure otherwise is identical with the 
method developed in this country. I am 
not, therefore, inclined to yield to it the un- 
hesitating deference which has become cus- 
tomary. There can be no doubt, in view of 
the splendid facilities due to the cooperation 
of the Royal Prussian porcelain works—fa- 
cilities which those who have been bafiled 
by porcelain technology, or have had to 
coax unwilling manufacturers into reluctant 
compliance, will appreciate—that the data 
of the Reichsanstalt will eventually be 
standard. For the present, however, I 
should be more impressed by some sterling 
novelty either in the direction of a larger 
range of measurement or of method. Con- 
ceding that an accuracy of 5° at 1000° has 
been reached, all results above 1500° re- 
main none the less subject to increasingly 
hazardous surmise. 
A beautiful method of absolute thermom- 
etry, albeit as yet only partially developed, 
is due to Topler. In this the densities of 
communicating columns of gas are com- 
pared very much as in Dulong and Arago’s 
classical methods for liquids, by the gravi- 
tation pressures which correspond to these 
unequally hot columns. To accomplish 
such extremely fine pressure measurement, 
SCIENCE. 
. high temperatures. 
[N.S. Von. VI. No. 140. 
Tépler invented the ‘ Druck libelle,’ an in- 
version, as it were, of the common level, in 
which, therefore, the motion of the bubble 
(or of a thread of liquid) indicates a change 
of pressure conditioned by the invariable 
horizontality of the instrument. 
The development of the practical forms 
of continuous intrinsic thermoscopes (the 
radiation, the thermo-electric and the elec- 
tric resistance methods) went, more or less, 
hand in hand with the development of the 
air-thermometer, although the latter is de- 
cidedly the more recent. Aside from pio- 
neering experiments of Muller (1858) and 
others, the well-known Siemens resistance 
pyrometer (1871) was the first instrument 
in the field. It was based upon data ob- 
tained from platinum, copper and iron by 
the calometric method of calibration. This 
instrument has been remarkably perfected 
by Callendar and Griffiths, using specially 
pure platinum calibrated by comparison 
with the air-thermometer as far as about 
600°. Notwithstanding these improvements, 
the resistance pyrometer is inferior, in my 
judgment, to the thermo-electric pyrometer, 
from the greater bulk and fragility of the 
exposed parts and the tendency of platinum 
to disgregate or waste itself gradually at 
Its upper limit of tem- 
perature measurement is thus limited; for, 
even if the difficulty of selecting suitable 
terminals for the coil is set aside, the diffi- 
culty of finding an insulator at very high 
temperatures would remain. According to 
Holborn and Wien resistance is seriously 
subject to the influence of furnace gases, and 
permanence of the low temperature con- 
stants does not imply a like permanence of 
the high temperature constants of the 
metal. 
Radiation pyrometry, curiously enough, 
is the most venerable method within the 
whole scope of the subject. It was intro- 
duced by Newton (1701) in his scala grad- 
wum caloris in connection with his well- 
