444 
POPULAR SCIENCE REVIEW. 
the thin stratum of interposed alcohol. The thermometer is protected from 
external injury hy enclosing it in a suitably constructed copper case, open at 
top and bottom, for the free passage of the water. In order to test the 
efficacy of this plan, the instruments to be tried were enclosed in a strong 
wrought-iron cylinder fflled with water, and submitted to hydraulic pressure 
which could he raised gi*adually till it reached three tons upon the square 
inch, and the amount of pressure could he read as the experiment proceeded 
upon a gauge attached to the apparatus. Some preliminary trials made 
showed that the press would work satisfactorily, and that the form of ther- 
mometer proposed would answer the purpose. These preliminary trials 
showed that, even in the thermometers with protected hulhs, a forward 
movement of the index of from 0-6° to 1° Fah. occurred during each experi- 
ment. This, however, Dr. Miller believed was caused, not hy any com- 
pression of the bulb, hut by a real rise of temperature, due to the heat 
developed hy the compression of the water in the cavity of the press. This 
surmise was shown to he correct hy some additional experiments made 
to determine the point. — Vide Proceedings of the Royal Society, June. 
Physics at the British Association. — Among the many papers read at the 
Exeter meeting, the follovdng are of interest : A Self-recording Hygro- 
meter. — Mr. Vivian described this. At a former meeting he exhibited a 
self-registering instrument on the cumulative^principle of recording mean 
values of the differences between wet and dry bulb thermometers, and a 
self-registeiing maximum and minimum hygrometer. He now produced an 
improved form, with a series of curves showing the comparative results of 
Leslie’s liygrometer, his maximum and minimum differential, his mean self- 
registering, wliich he now offered as the standard. He gave the uses to 
which it might be put. He had used it in recording the aggi’egate differ- 
ences of solar heat of the sun and shade, the duration of rain, and the 
amount of nocturnal radiations, and many other similar purposes. He now 
proposed to apply it to recording the actual mean temperature, which would 
be an important feature, if it could be worked out, and he believed it could, 
and also to tlie anemometer. A Neio Anemometer. — A rough model of an 
instrument of this kind was exhibited by Mr. C. J. Woodward. A Self- 
recording Aneroid Barometer. — This instrument, which is manufactured by 
the Stcreo8CO])ic Company, consists of a handsome combination of eight day 
clock and aneroid. The clock works a revolving cylinder on 'yvhich a pencil 
carried from the aneroid by weight and pully records the daily pressure of 
the air. Ruck- salt IVisms . — Mr. Charles Brooke gave an account of his 
rock-.-alt prisms. He said that, in his attempts to grind and polish rock- 
salt prisms in planes not parallel to the lines of cleavage of the crystal, he 
found that the partly -ground prisms usually cracked and broke at the 
thinnest end. He and Mr. Browning, the optician, consequently tried the 
plan of slowly heating the rock-salt buried in sand in a tin vessel, and then 
permitted the whole to cool very slowly. After this annealing had been 
performed, it was possible to giind the rock-salt into good prisms. 
Mr. Browni/a/x cheap Aneroid. — Mr. Browning has brouglit out an aneroid 
barometer of so convenient a size, so accurate in registration, and so cheap, 
that wo cannot help calling the attention of our readers to it. We have 
had the instrument under observation for a long while, and can speak from 
experience of its merits. 
