Rain, by the pluviameter, between noon the 1st of Dec. 1818, and noon the 1st of Jan. 1819, 1.215 inch. The quantity that fell on the roof of my Observatory, during the same period, 1:231 inch. Evaporation between noon the 1st of Dec. 1818, and noon the 1st Jan. 1819, 0.53 inch.

ARTICLE XIV.

METEOROLOGICAL TABLE.

BAROMETER. THERMOMETER. Hygr. at

1818. Wind. Max. Min. Med. Max. | Min. Med. 9 a. m.

Rain.

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 column. A dash denotes, that the result is included in the next following observation,

REMARKS.

Twelfth Month.-21. Much wind about three, a. m. with a little rain: a very fine day ensued: Cirrocumtulus, with bright sunshine. 22. White frost: foggy, a. m.: clearer, p. m. with Cirrus: rime on the trees. 23. White frost: rime to the tree tops: misty, a. m. : sun very bright at noon: much fog to the south. 24. Very foggy: rime still on the trees. 30. White frost. 31. A very fine day. 1819. First Month.-1. Very foggy, with the addition of obscurity from smoke. 3.air: rather overcast sky. 4. Much rime on the trees: rather misty air. 5. Somewhat misty: the melted rime forming puddles under the trees. 6. Fine day: at night, small portions of cloud were observed to pass swiftly under the moon. 7. The sun-rise was attended with a veil of Cirrus clouds passing to Cirrostratus, very red and lowering: about noon came Cumuli and other clouds, with a gale and showers. 8. Fine day night windy, with some rain. 9. Hazy, a. m. with Cirrostratus and wind: heavy showers, p. m.: very clear night. 10. Overcast soon after sun-rise, with wind: the fore part of the night very stormy. 11. A wet squall this morning: fair day, with Cirrus and wind. 12. Fair morning, with slight hoar frost: the gale has subsided. 13. Slight hoar frost: very fine day: at evening, windy again. 14, 15. Windy, with some showers. 16. A fine drying wind, a. m. with Cirrus and Cirrostratus in delicate striæ; also transient Cirrocumulus at a great elevation: a stormy night followed. 17. A very tempestuous day the rain ceasing for a while, a. m. I observed Cirrostratus around large Cumuli, rising and separating, as if the shower had been produced by their previous inosculation: much wind in the night. 18. A fine, drying day, with the wind more moderate, and an overcast sky.

:

RESULTS.

Winds Variable and gentle, with fogs in the fore part; in the latter, strong southwest gales, with rain.

ANNALS

OF

PHILOSOPHY.

MARCH, 1819.

ARTICLE I.

Researches on the Measure of Temperatures, and on the Laws of the Communication of Heat. By MM. Dulong and Petit.

(Continued from p. 124.)

Of the Dilatation of Solids.

IF we compare the results of the preceding table with those that we have given in Table I, it will be seen that the doubts which we raised respecting the rate of the mercurial thermometer were not without foundation; and that the laws of the dilatation of the envelope of this instrument, and of the liquid which it contains, are very distinctly different, when we consider a great interval of temperature. When the air thermometer marks 300° on its scale, mercury taken absolutely would mark 314-15°; while the common thermometer only marks 307·64°. The preceding determinations are so much the more interesting, because they may lead to the knowledge of the absolute dilatation of several solid bodies. Nothing more is necessary than to ascertain the difference between the expansion of mercury and each of these bodies.

This is easily obtained with respect to glass; for the difference in question is merely the apparent dilatation of mercury in that body. Though this dilatation has been already the object of a great many determinations, we have thought it necessary to undertake it ourselves with all the care that such experiments require. For this purpose, we employed a tube of about 6 decimetres in length, and capable of holding about 700 grammes of mercury.. This tube was shut at one of its extremities, and VOL. XIII. N° III.

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