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The observations in each line of the table apply to a period of twenty-four hours, beginning at 9 A, M. on the day indicated in the first colum 1. A dash dengies that the result is included in the next following observation.

REMARKS.

Third Month.-1. Fine. 2. Cloudy. 3. Drizzling rain : a furious gale of wind from the NW all night. 4. The wind continued to blow with great violence all day. 5, Fine. 6. Cloudy: bleak. 7. $nowy. 8. Cloudy. 9. Fine. 10. Rain. 11, 12. Fine. 19—15. Cloudy. 16. Fine. 17. Cloudy. 18. Drizzly. 19: Snowy morning a very cold wind NE in the night. 20. Snow in the morning : afternoon rainy: a lunar halo in the evening. 21. Drizzly. 22. Overcast. 23-26. Cloudy. 27. Cloudy: night foggy. 28. Cloudy and fine, 29. Cloudy. 30, 31, Fine.

RESULTS.

Winds; N, 4; NE, I ; E, 5; SE, 2; SW, 5; W, 2; NW, 12.

Barometer: Mean height
For the month.

29.952 inches. For the lunar period, ending the 4th. .....

29•676 For 15 days, ending the 12th (moon south) ...... 29•698 For 13 days, ending the 25th (moon north) .......

30.049

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A new and easy Method of ascertaining the Degree of Tempera

. ture at which Water is at its Maxinum Density. By Mr. James Crichton.

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(To the Editor of the Annals of Philosophy.) SIR,

Glasgow, May 2, 1923. Having lately been much engaged in determining the specific gravities of certain fluids, by means of adjusted balls of glass, and being satisfied that for simplicity and accuracy, no method whatever is nearly so good; I was led to think, that another important point could thereby with greater certainty be ascertained, than by any mode yet adopted. This is to determine the temperature at which water attains its maximum density.

Of all who have hitherto attempted to decide this question, whether British or foreign philosophers, no one seems to speak with the precision which might be desirable, of the degree at

, which the phenomenon takes place. The French say it is between 4 and 5 of Celsius, thus admitting an uncertainty of about 2° of Fahrenheit; some in our own country think it is at 39, while others place it at 40. Any person who is aware of the many sources of

error,

and of the vague nature of the requisite compensations, will not wonder at this indecision; the difficulty alone, of maintaining an uniform temperature, throughout a large or deep body of water is very considerable ; hence the bulkiness of the solíd used by

New Series, vol. V.

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the French for this purpose, having been a cylinder nine inches in diameter, and of the same height, must have rendered it a matter of uncommon difficulty in the quantity of water necessary. Whether this uniformity existed, at the moment of its greatest apparent gravity, may admit of some doubt, however carefully and constantly the thermometer may have been observed ; besides, air-bubbles, which it would be almost impossible to see or remove, might have considerably increased the buoyancy of the suspended solid. To estimate the compensations for expansion, in the above-mentioned method, is perplexing, and for the mode by the weighing bottle is still more so; but to ascertain the quantity of hygrometric humidity, which profusely and rapidly fixes on the exterior surface of a bottle, at so low a temperature as 40, is perhaps from several causes impracticable. A hope of being able to assist in obviating these embarrassments, induces me to present a new method of determining this point.

Having frequently, observed that a very small alteration of temperature in a fluid, destroyed the precise poise of a solid in that fluid, and that an extremely minute increase or diminution of gravity in the solid, has a similar effect; it was easy to perceive, that if water is of a certain gravity just above freezing, and that if it become heavier, with an increase of temperature, before it reach, say for example, 50, then it is manifest, that at some included degree, water must of necessity poise, or sustain, a ball or solid of greater specific gravity, than it will do at any other point in the supposed interval.

My first attempt to ascertain this point, evinced, that a ball which was just poised, at about 33, had the same property near 51; this gave 42 for the point of greatest density, taking the half of the intervening degrees as additive to 33, or the reverse from 51, since all authorities seem to agree, that the expansion is the same for equal intervals of temperature, on both sides of the maximum.

It may be supposed, that to adapt a ball of the greatest possible specific gravity which water can sustain at its greatest gravity, would be the next endeavour; it was, but so infinitely little is the variation of the gravity of water, for about a half degree on either side of the maximum point, that although I have, more than once, diminished the gravity of balls which were too heavy, by a quantity so minute, as not to amount to the 6000ths part of a grain, or just as little as I could by any means grind off, still, on trial at the proper range of temperatures, it was found that the mark had always been overshot. This then was relinquished as a hopeless task.

As it had not however escaped notice in the course of these experiments, that the further the temperature of water was removed from that of the greatest gravity, the ball rose, or fell

, with celerity just commensurate to the number of degrees which

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the existing temperature was above, or below, that of the desiderated degree: this, therefore, affords some idea of the approach to, or retrocession from, the temperature in question; but there is a better, and perhaps conclusive proof of its place in the scale, which I shall now describe.

I took a glass jar; 2 inches in diameter, and 3 in depth'; into this was put distilled water to the depth of 24 inches, and cooled down to near the freezing point, but carefully prevented from congealing, as the disengagement of air-bubbles from the ice, when fluidity took place, would have frustrated the experiment; into this was put a ball

, previously well wiped with a silken * cloth, and immediately, by means of a clean hook of glass, lifted, but not rapidly, twice or thrice out of the water; this cleared it of any air-bubbles, which though imperceptible, might have been adhering to its surface. The ball now fell to the bottom of the jar, which as usual was convex, but had a small flat surface on the summit, to which the ball was led, and there it rested. In the water there were suspended two very accurate and sensible thermometers, the bulbs being at the middle of the water as to depth, and just so far removed

from its diametrical centre, as not to be in the path of the ball when it rose.

In these circumstances, the lower end of the ball was care: fully watched with a large reading glass, and at the moment of its quitting the bottom of the jar, the thermometers were examined, and the degree noted; when the ball had risen about one-fourth of an inch a small rod was cautiously let down, and without agitating the water, gently made to touch the ball; it of course descended, but instantly rose; this is a very delicate part of the experiment, and if overdone loses its effect. It was fres quently repeated, and the ball always reascended with accelerated velocity

The thermometers indicating an increasing temperature, the ball finally became stationary at the surface of the water ; from time to time it was slightly touched as before, but in proportion as the temperaturè rose beyond a certain point, the tendency of the ball to ascend, after these strokes, obviously diminished, judging by the velocity with which it did so ; its upper extremity, when examined with the magnifier, plainly seemed to

it were more and more feebly on the surface of the water, till at last, a fine thread of separation became visible ; the degree by the thermometers was again marked, and as they continued slowly to rise, the ball gradually fell to the bottom of the jar.

From many similar experiments I have concluded that 42 is extremely near the true point of the greatest density of water; my most satisfactory trials never gave 3-10ths of a degree less

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In an experiment of such delicacy, this must be attended to, as linen never fails to leave fibres on whatever is wiped with it; these will detain air enough to render the efforts of the experimenter in this case abortive.

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