395 
1909-10.] Proposal for a Portable Barometer. 
delicate adjustment can be effected by sliding the Six’s thermometer a little 
up or down, thereby altering the zero point on the air thermometer and the 
standard pressure under which the instrument is issued. It is of no im- 
portance what the exact value of that pressure shall be. 
The other arrangements are simply for the purpose of mounting the 
various parts in rigidly fixed positions, for proper illumination, and for pro- 
tection from damage in travel, and need not be described in detail. An 
instrument that will read from 31 inches to 22 inches pressure between 10° 
and 120° Fahr. will be about 15 inches in total length. 
It need hardly be pointed out that the Six’s thermometer can be used in 
the usual way as a maximum and minimum thermometer when a station is 
occupied for twenty-four hours. The two bulbs are enclosed in a thin metal 
case polished outside and blackened inside. 
It is proposed to call the instrument a thermobarometer. 
PS., January 24, 1910. — The usefulness of the barometer in field practice 
will be determined very largely by its portability ; and it is realised that the 
Six’s thermometer, and probably also the air thermometer, may require to 
be modified in the light of actual experience. 
There is a superficial resemblance between this instrument and the 
sympiezometer invented by Adie and described by Dr Buchan in the 
article “ Barometer ” in the ninth edition of the Encyclopaedia Britannica. 
Both take advantage of the expansion and contraction of air under the 
combined influence of changing pressure and temperature. By means of 
an attached thermometer and sliding scale, Adie applies a correction for 
temperature, and thereby deduces the barometric pressure. In the 
instrument described in this paper the mass of air is brought to a 
definite pressure, and the mercury column, which partly supports this 
pressure, at once gives by its length the acting pressure of the atmosphere. 
The novelty in the construction of the instrument is the device for securing 
that the air has been brought to the chosen definite pressure. In the 
principle of its action as well as in the arrangement for carrying this 
principle into effect the “ thermobarometer ” differs fundamentally from 
the sympiezometer. 
(Issued separately May 7 , 1910 .) 
