Papers on meteorology : relating especially to the climate of Britain, and to the variations of the barometer / by Luke Howard.

  • Howard, Luke, 1772-1864.
Date:
1850-1854
Catalogue details

Licence: Public Domain Mark

Credit: Papers on meteorology : relating especially to the climate of Britain, and to the variations of the barometer / by Luke Howard. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    7. The fifth column of Table II. contains the barometrical mean, calculated upon the whole period of solar years, which, in the four preceding columns, are averaged under the respective lunar positions of north, south, &c. The sixth column of this Table shows a mean founded on a direct average of the four results placed under these heads. I have noticed some features of the variation at the foot of the Tables. I shall proceed now to state some general results, of course as to the barometer alone. The effects on the mean temperature and rain must for the present be left unnoticed*. Tice barometrical mean in our climate is depressed (on an average of years) by the moon s position in south declination. In every one of these averages upon periods of nine years, in Table II., the mean under south is lower than that under north declination ; the difference being in some cases between six and seven hundredths of an inch: and it is larger on the averages in the fore-part than on those in the latter part of the series. The mean under south declination is also lower than either of the other three; with exception of the four latter averages, in which it exceeds a little that of the position “ going south.” This depression is gradual: it commences with the moon in full north declination, and proceeds through her remaining positions to the time when she again crosses the equator to return north; at which season the whole weight that had been abstracted is suddenly restored—this of course must be understood of the small differences in the mean here treated. There will be found, in the observations employed, an abundance of particular cases of variation which contradict such a rule, but the com- pensations, it appears, cover these in its favour. We have here, I think, evidence of a great tidal wave or swell in the atmosphere, caused by the moon’s attraction, preceding her in her approach to us, and following slowly as she departs from these latitudes. Were the atmosphere a calm fluid ocean of air of uniform temperature, this tide would be manifested with as great regularity as are those of the ocean of waters. But the currents, uniformly kept up by the sun’s varying influence, effectually prevent this, and so complicate the problem. There is also manifest in the lunar influence a gradation of effects, which is here shown, as it is found to operate through a cycle of eighteen years. In these, the mean weight of our atmosphere increases through the fore-part of the period; and, having kept for a year at the maximum it has attained, decreases again through the remain- [* They are discussed in the succeeding paper, p. 43a.]