SEPTEMBER 3, 1897. ] 
if one uses these data for a given gas to 
compute the contestants in Van der Waal’s 
law, one is actually able to predict remote 
eritical conditions of the gas in question 
with a fair order of accuracy. 
Whenever pressure measurements are to 
be made through such large intervals as are 
here in question, the elastic constants of the 
apparatus become of increasing moment. 
Amagat, however, treated these incidental 
measurements as of like importance with 
the rest of his labors. The starting point 
of his investigation into high pressures was 
the open mercury manometer first erected 
along a staircase near Lyons, finally in the 
shaft of the St. Htienne mine, about 380 
meters deep. This apparatus was used for 
graduating the closed manometer, prefer- 
ably containing nitrogen. In later experi- 
ments for excessively high pressures the 
closed manometer was replaced by the 
‘manométre a4 pistons libres,’ a sort of in- 
verted Bramah press, in which the small 
pressures of an open mercury manometer 
acting on a large piston compensate the rel- 
atively large pressures of the piezometer 
acting on a small piston. The ingenious 
feature of Amagat’s apparatus is the rota- 
tion of both pistons just before measure- 
ment, a device by which friction is rendered 
harmless. Equipped with this instrument 
direct determination of the bulk modulus 
for glass and metal was actually feasible. 
In the ease of glass no serious variation of 
’ the compressibility could be ascertained 
within 2,000 atmospheres, and even 200°, an 
observation of great value in practical re- 
search. Poisson’s ratio was similarly de- 
termined and the data used in computing 
Young’s modulus. But the most important 
result of these researches, a result to which 
Professor Tait also contributed, is the 
datum found for the absolute compressi- 
bility of mercury. This will enable all fu- 
ture observers in piezometry to standardize 
the apparatus with ease and nicety. 
SCIENCE. 
dol 
Time prevents me from dwelling upon 
the remaining investigations of Amagat in 
a measure commensurate with their value. 
These contain a counterpart for the liquid 
state of the results already announced for 
gases. The change of volume throughout 
enormous pressures and about 200° of 
temperature is considered in detail for a 
number of important liquids. Only in one 
case, and that the rather remarkable one of 
carbon tetrachloride, are evidences of solidi- 
fication encountered and the conditions de- 
termined. Amagat believes the absence of 
solidification to be due to the occurrence of 
the lower critical temperature below the 
isothermal of compression. In my own 
judgment, however, the pressures necessary 
to reach this lower critical point will be 
enormous eyen in units of 1,000 atmos- 
pheres, for which reason it is not in any 
case liable to be an easy conquest. 
Special mention finally is due to the 
thermal position of the maximum density 
of water, which Tait had already studied. 
Amagat shows definitely that the tempera- 
ture of maximum density moves towards 
the freezing point with increasing pressure, 
so that at high pressures, as well as at high 
temperatures, the behavior of water loses 
its anomalous character. In general, com- 
pressibility and expansion decrease with 
pressure for all normal liquids, and expan- 
sion increases rapidly with temperature. 
Other anomalous properties of water have 
been investigated, among which the dimin- 
ished viscosity of water under pressure at 
ordinary temperature studied by Rontgen, 
Cohen ‘and others may be stated. 
After this cursory and wholly inadequate 
mention of the work of Amagat and the 
physicists who, like Tait, Cailletet and 
others, have been engaged in closely allied 
researches, it will repay us to look at some 
of the other as yet less splendidly developed 
contributions to piezometry. At the outset 
it is well to make mention of the forms of 
