This land was worth about 5s. per sta- Expenses of 13 statute acres covered with £. s. d. 434 7 10 This land was worth about 3s, per acre, Expenses 2 statute acres of land fenced out, and sets found for many poor people to plant for potatoes at 10%. per acre. This land was worth about 2s. per acre 294 18 0 20 Expenses 3 statute acres of land planted This land was worth about 2s. per acre Expenses 26 statute acres levelled and drained with open and covered drains, at present very dry, and the 60 0 0 200 00 acre, Total £.1009 5 10 Experiments Experiments and Observations on the Heat and Cold produced by the Mechanical Condensation and Rarefaction of Air. By JOHN DALTON. From the MEMOIRS of the LITERARY and PHILOSOPHICAL SOCIETY of MANCHESTER. IF a thermometer be inclosed in a receiver, and the air suddenly condensed, the thermometer rises a few degrees above the temperature of the atmosphere; and if the air be exhausted from a receiver inclosing a thermometer, the mercury sinks a few degrees immediately; but in both cases after some time it resumes its former station. These facts are well known to philosophers of the present age, but they do not all agree in the explanation of them. Thinking the subject worthy of elucidation, I was duced to institute a series of experiments for the purpose, which I apprehend have led to a clear demonstration of the cause of the phenomena, and moreover make the facts themselves appear in a somewhat different point of view from what they are seen in at the first moment in One circumstance is very remarkable, that whether the mercury rises or falls in these instances, it is done very rapidly; whereas in the open air, if a thermometer be only two or three degrees above or below the temperature, it moves very slowly. This seems to have suggested to every one the idea that the elasticity of the glass bulb of the thermometer has a principal share in producing the effect, by causing the bulb to yield a little to the pressure of the air. It has however been found upon trial, that the same effects take place whether the thermometer is sealed or not. My experiments accord with this, having made a thermometer and left it unsealed for the ex press press purpose; in all the experiments with condensed and rarefied'air, there was no sensible difference observed to arise from the inequality of pressure on the external and internal surfaces of the bulbs, the sealed and open thermometers varying the same in kind and also in` degree, except from circumstances to be noticed hereafter, It being certain then that a real change of temperature takes place, it remained to determine the quantity and manner of that change. Having chosen a small, and consequently sensible thermometer, with a scale of degrecs sufficiently large to admit of distinguishing onetenth of a degree, I proceeded to ascertain several facts experimentally. Experiment I. Took a receiver, the capacity of which was about 120 cubic inches, and suspended the thermometer with its clear bulb in the central part of it; then letting the whole acquire the temperature of the room, which was without a fire, I exhausted the air, and afterwards restored it, marking the effects upon the thermometer. The medium of several trials, nearly agreeing with each other, was as under: rose when the air was restored to . 38 .9 The suddenness of the fall and rise puzzled me most: after reflecting upon it for some time, I conjectured that the real change of temperature of the air or medium wast much greater than the thermometer indicated, but that the inequality existed only for a few seconds of time, because the receiver, &c. immediately impart beat to, or abstract it from, so small a quantity of air as 120 eubic inches, which are only equal to 40 grains in weight. The The phenomena of the thermometer seemed very well to accord with the supposition of great heat or cold acting upon it for a few seconds only. Experiment II. Pursuing this idea, I imagined that if two thermometers, whose bulbs were very unequal in magnitude, were inclosed together, the smaller bulb ought to give the greater variation: accordingly I inclosed two, the diameters of their bulbs being .35 and .65. of an inch respectively; and having exhausted the air, and restored it again repeatedly in succession, and found a mean of the variations, that of the small bulb was 20°.8, and that of the large 2°.2. Experiment III. Repeated the exhaustion with the sinall thermometer, inclosed in three different circumstances successively; 1st, with the bulb in the centre of the receiver; 2d, with the bulb re ting on the wet leather › of the plate; and, 3d, with the bulb resting against the side of thr receiver. Experiment IV. Inclosed a wine glass with about a cubic inch of water in it, containing the bulb of a thermometer, in a receiver; and, exhausting the air, the thermometer sunk half a degree suddenly, and then continued stationary; upon restoring the air it suddenly rose half a degree. All these experiments confirmed my conjecture of a much greater degree of heat and cold being produced in these cases than the thermometer points out, but that its continuance |