28 REPORT—1849. 
British Isles extended and completed,—all Ireland and Wales, as well as the north- 
western part of Scotland, exhibiting as yet great blanks on an isothermal map. 


Contributions to Anemometry— The Therm-anemometer. By JouN PHILLIPS, 
F.R.S., Assistant-General Secretary to the British Association. 
The author’s researches into the force and velocity of wind have been directed to 
the completion of a method of wind-registration which should be independent of 
mechanical movements, momentum and friction *. He wished to register the wind 
by one of the effects of the displacement of its molecules, not the movement of its 
mass. For this purpose only one method has occurred to him as sufficiently appli- 
cable, viz. the evaporation of a liquid. He has experimented on water, saline 
solutions and alcoholic mixtures, and he finds that with either of these liquids an 
instrument really indicating the movement of wind, by the registration of the eva- 
poration which the wind causes, is producible. Such an instrument 
need occupy but a very small space, and will have the desirable quality 
of being most accurate in those very low velocities of wind which elude 
entirely Lind’s anemometer, and are scarcely sensible by any register- 
ing machinery. 
It will be remembered, that for the interpretation of the register of 
evaporation into a register of wind velocity, it was necessary first to 
correct for the hygrometric state of the air. This being done, the cooling power of 
wind was found by experiment to be nearly as the square root of its velocity. In 
this experimental result Professor Phillips was induced to place confidence, because 
it appeared to represent and flow naturally from what may be thought the true phy- 
sical action of the moving air. 
Having lately occasion to examine extensively and carefully into the amount of 
air which passes through the ramified passages of collieries, where the currents are 
sometimes so slow, that machine anemometers, even of a most delicate description, 
are insensible to the movement of the air-—where even the miner’s candle affords but 
a rude guess, and where the situation is such that smoke or the powder flash can- 
not be appealed to—he was happy to find that the problem was perfectly and easily 
solved, by noting the cooling power of the current. 
For this purpose a registering or integrating anemometer is not required. The 
currents underground are steady, and require only an anemoscope or indicator of 
the momentary velocity. Evaporation from the wet-bulb may therefore be aban- 
doned ; the common thermometer, with its bulb clear of the frame, will answer the 
purpose of experiment in every conceivable instance fF. 
The author stated the general formula, to which he had been conducted by very 
numerous experiments through a large range of velocities ascertained by other means, 

thus: ——r=v. 
2 
In this formula C and r are constants to be determined for the particular ther- 
mometer in use; s being the number of seconds which elapse in cooling through a 
certain range (5°) from a point a certain number of degrees (10°) above the tempe- 
rature of the moving air, » the movement of air in a given time (one second). 
The explanation is simple. A thermometer-bulb, heated above the temperature 
of the surrounding air, is cooled by radiation and by convection. 
Omitting at present the consideration of the cooling in the thermometer-bulb by 
radiation (r), the effect of air movement in lowering temperature is proportional to 
the quantity of air (q) (or number of cooling elements) which passes the bulb, and to 
the time of its action (s), or to'gs, which will be aconstant (C) for each instrument. 
The quantity which passes is proportional to the velocity of the current, and to the 
time of its action, org=vs. Hence C=qs=vs", andv= = 
* Reports on Anemometry, 1846, p. 340; 1848, p. 97. 
+ It appears from Prof. Forbes’s Report on Meteorology to the British Association in 
1832, that the idea of employing a thermometer for indicating the velocity of wind was en- 
tertained by Professor Leslie. It appears never to have been worked out.—(J. P.) 


