In the figure o posite are represented, against a portion of the barometrical scale, the following particulars, deduced from the ten years observations from 1807 to 1816.

1. By the full curve above passing through them, the average of the ten maxima, or highest observations, in each month in those years.

2. By the full curve below, in like manner, the averages of the ten minima, or lowest observations.

3. By the dotted perpendiculars, the mean range in its place in the scale, which was exhibited after a different manner in the former figure.

4. By the dotted curve passing through the middle point of each of these, the actual additions to the weight of the air in the summer months, from vapour sustained by the heat; and independent of the effects of opposite winds above mentioned. See page 78.

g. Curves on a large scale exhibiting these differences would be instructive: they might be made from Meteorological Registers kept in different latitudes, which are published in various periodical and other works.

h. It is possible that, of two Barometers made perfectly alike or comparable, the one placed within the atmosphere of a city or town might be found always higher, from the weight of the smoke and vapours (at the same hour and temperature,) than the one in the clear air of the country. And it might be affirmed (with as much truth as we say the Earth moves towards the falling body), that the flight of every bird across the field adds to the weight supported, and so to the height of the column.

i. Clim. Lond. i. 298-303.

It may be convenient, here, to use for demonstration the annexed figure, on a large scale, of the Barometical variation through a space of eleven days. See Clim. Lond. ii. 31.

1807 Nov. 10 11 12 13 14 15 16 17 18 19 20

1807. Nov 10 to 20-part of a windy period of 28 days from New M. to New M., the mean of which is 29.47 in. represented by the horizontal line; the curve passes through the mean height of the Barometer for each day.

Southerly winds had prevailed from the 28th Oct. with about an inch of rain: the temperature had gone down since the first of the month, from 54° to 44o in the max. and from 43° to 33° in the min. Thus circumstanced as to the previous weather, a south-east wind on the 10th brought 0.61 in. of rain: after which, the wind changing to N.W., we see the Barom. rise an inch (on the mean) in three days, going to about 30 in. A little snow followed the before-mentioned rain, and it froze on four successive nights, the first ice of the season--the wind N. and N.E. The wind now changing to southward, the Barometer falls rapidly between the 17th and 20th; snow falling on the 19th in considerable quantity, dissolved by rain in the course of that day-the whole making about half an inch in the gauge.

We thus have the curve at 29 in. -a depression not only attended with snow and rain, but introductory to a second rain of like amount: after which came a smart frost, with a turbid atmosphere and frequent intermissions of the cold, continued through the greater part of December. The Evaporation during these eleven days was about six tenths of an inch: it lessened much before the rain, and increased after it. The total rain of the period of 28 days,

near London, was 2.83 in.: but at Manchester in the same time there fell about five inches, the mean temperatures being nearly alike. Such is the history of ten days' weather, studied in this interesting manner: a thing which every one possessed of the requisite instruments, and the daily leisure to observe them, may at any time do for himself. See for the rest Clim. Lond. ii. 31. It was found by observations carefully made in 1807 and 1808, near London, that the rain which fell by day was to that which fell by night as 2 to 3 in amount, nearly. Idem. i. 110.

k. See the autumnal periods of the Register in vols. ii. and iii. of Clim. Lond. passim.

7. Clim. Lon. ii. 7, and the Register passim.

m. Idem. in the Register at large, passim.

n. Idem. in the earlier periods of the Register, under the head of Evap. in the 2nd volume.

o. Idem. vol. i. p. 312: and 81-88.

p. The annexed is the figure of the scale for an Evaporation-guage.

See Clim. Lond. Intr. xvi. and i. 97.

q. Another form of the gauge, consisting of a cylindrical glass and small five-inch cistern, is represented p. 192. Note, that the glass cylinder is graduated also for the Rain, but in the reverse direction. For evaporation the full scale is put into the cistern, and the quantity lost by drying ascertained by returning the residue into the glass. The amount of Rain (through a funnel of five inches) is seen on inspection, when the water is put into the glass. The figure of the rain-bottle and funnel is further on.

*. Clim. Lond. Intr. xiv. and i. 89. See on this subject the practical observations of Mr. Marshall, in his ""Minutes, &c. on Agriculture in the Southern Counties." 1799. vol. ii. 209, 232. He says in one place, I went up to a distant part of the farm and took the teams into the field, merely on the indications of the Hygrometer; and found the peas [which had been on the preceding morning soft] perfectly fit to be carried.' He used a hygrometer of his own making; of stout whipcord, five feet long, connected with an index traversing a scale on the segment of a circle. The whalebone hygrometer is a neater instrument, and will remain longer serviceable.

s. Clim. Lond. i. 99. 108-110.