OBSERVATIONS ON THE BAROMETER, THERMOMETER, & RAIN At Manchester, FROM THE YEAR 1794 TO 1840 INCLUSIVE, BEING A SUMMARY OF ESSAYS ON METEOROLOGY. BY JOHN DALTON, D.C.L., F.R.SS. L.& E., MEMBER OF THE INSTITUTE OF FRANCE, &c., &c. (Read at various times, from the year 1830 to 1840.) Ar the close of the year 1818, I read an epitome of my meteorological observations for the preceding twenty-five years: these were afterwards printed in the third volume (new series) of the Society's Memoirs.* Such a lengthened series of observations could not fail to suggest inferences of a theoretical nature; some of these * In the essay above alluded to, I had occasion to refer to the transactions of the Royal Society of London for a series of observations of the like nature; and, upon a comparison. of those with my own, I found reason to believe that the Royal Society's observations and calculations from them, exhibited marks of carelessness which rendered them by no means trustworthy. I intimated the same in a note (see page 490 of the above-mentioned volume.) Some time after this, were advanced and corroborated by the results of other Meteorologists. Since that time the period has been extended by the addition of twenty-two years more; and it is proposed in this communication to give a summary of the observations made in the last-mentioned period, and then to incorporate the results with those of the former period, so as to obtain averages for the entire of both periods. If there is any natural tendency in the state of the atmosphere to produce rain (or any other phenomenon) more at one time of the year than another, it will be shewn by the observations of a few years. Ten or twelve successive years are almost certain to produce a good outline of the characteristic features of the year; but it may require half a century or more to obtain an exact delineation of them, and such as would render future observations of little or no avail in producing any sensible alteration. This observation is applicable to the fluctuations of the atmosphere the Royal Society revised their Meteorological establishment, and placed it upon a most respectable footing, since which, I believe, they may vie with any public body, or private individual, in the regularity and accuracy of their observations and tabular results; and, I may add, that I have consulted them with pleasure and advantage since on several occasions. in weight, as shewn by the Barometer, and to the temperature of the atmosphere, as well as the quantity of rain, and to the other meteoric phe nomena. 1. OF THE BAROMETER. Experience proves that the weight or pressure of the atmosphere on the earth's surface is continually varying from winds and other causes; and there is reason to believe that changes of weather are in some way connected with these fluctuations in the weight of the atmosphere, and hence the utility of Barometrical Observations. In the Torrid Zone the variation is little; in the Temperate Zone the variation is much greater; it increases with the latitude, and is about double in winter to what it is in summer, and it is probably still greater in the Frigid Zones. Many people imagine that the variations are local-that the Barometers may rise in one town, and fall in another neighbouring town at the same time. This is not the case; the variations take place in London, Penzance, Dublin and Edinburgh, at the same time, and to the same amount nearly. the number of observations. afternoon, and eleven in the evening. observations together, and dividing the sum by monthly averages were found by adding all the in the morning at eight o'clock, about one in the vations were made three times each day, namely, are contained in the following table: the obserThe results of my Barometrical observations The TABLE OF THE MEAN MONTHLY HEIGHTS AND ANNUAL HEIGHTS OF THE BAROMETER FOR TWENTY TWO YEARS, VIZ. FROM 1819 TO 1840 INCLUSIVE. Years. Jany. Feb. Mar. April May. June July. Aug. Sept. Oct. Nov. Dec. An. Mns. 1819 1820 1822 1823 1824 1825 1826 1829 1830 In. 29.98 29.94 30.02 29.90 29.95 30.02 30.04 29.97 29.94 29.90 In. In. In. In. In. In. In. In. In. In. In. In. 1831 1832 1833 1834 29.87 29.95 29.82 30.01 29.84 29.98 The same Barometer has been used during the last twenty-two years as was in use the fifteen preceding years. It stands nearly 1-10th of an inch higher than other good Barometers do in the same situation, probably from some difference in the mercury. I find the allowance I have made in the scale for the rise and fall of the mercury in the reservoir is rather too small; consequently, the extreme elevations and depressions are not quite so great as they ought to be, but the influence of this circumstance upon the averages is scarcely worth notice. Now, if we incorporate the means of the Barometer for twenty-two years, as above stated, with those of the former period of twenty-five years previously published, (see Vol. III. page 487,) so as to obtain general averages or means for both periods, amounting to forty-seven years, we shall obtain the following means for the different months, and the mean annual height of the Barometer for the whole period. |