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nic acid furnished by volcanoes, as at the expense of the carbonic acid furnished by animals themselves. It is not then for the purpose of purifying the air that these breathe, that vegetables are especially necessary to animals ; it is, above all, to furnish them incessantly with organic matter quite ready for assimilation : organic matter which they may turn to their advantage.

There is, therefore, a service necessary, without doubt, but so remote, that it can scarcely be recognised, which vegetables render us, in purifying the air which we consume.

There is another service, so immediate, that if, during a single year, it were to fail us, the earth would be depopulated ; it is that which these same vegetables render us by preparing our nutriment, and that of all the animal kingdom. In this, especially, is found the chain that binds together the two kingdoms. Annihilate plants, and the animals all perish of a dreadful famine; organic nature itself entirely disappears with them in a few seasons.

We have, however, said that the carbonic acid of the air varies from 4 to 6 10,000ths. These variations are very frequent, and very easy to observe. Is not this a phenomenon reproaching the influence of animals who introduce this acid into the air, and that of vegetables which deprive it of it ?

No; this phenomenon, you are aware, is a simple meteorological phenomenon. It is with carbonic acid as with aqueous vapour, which forms on the surface of the sea, to become condensed elsewhere, fall again in rain, and be reproduced under the form of vapour. This water, which is condensed and falls, dissolves, and carries with it carbonic acid ; this water, which evaporates, yields up the same

gas to the air.

A great meteorological interest would attach to the observation of the variations of the hygrometer, and those of the seasons, or of the state of the sky with the variations of the carbonic acid of the air ; but hitherto all tends to show that these rapid variations constitute a simple meteorological event, and not, as has been thought, a physiological event, which, singly considered, would infallibly produce variations infinitely slower than those which are, in fact, observed as much in towns as in the country itself.

Thus the air is an immense reservoir, whence plants may for a long time derive all the carbonic acid necessary for their wants ; where animals, during a much longer time, will find all the oxygen that they can consume. It is also from the atmosphere that plants derive their azote, whether directly or indirectly: it is there that animals finally restore it.

The atmosphere is, therefore, a mixture which unceasingly receives and supplies oxygen, azote, or carbonic acid, by means of a thousand exchanges, of which it is now easy to form a just idea, and the details of which a rapid analysis will now enable us to appreciate.

(To be continued).

Formation and Dispersion of a Thunder Shower ; Parhelia, and

Meteorological Register. By Willis GAYLORD. * In looking over my meteorological notes for 1839, under date of August 21st, I observed the following :" Witnessed the formation and dispersion of a thunder shower, attended with some remarkable phenomena ;" and as the formation and action of clouds and storms is always an object of interest, I have thought a description of the one alluded to might not be altogether without its claims to notice.

The wind on the 21st and for two days previous had been southwardly, most of the time S. E. The 20th was one of the warmest days of the season, the thermometer at 2 o'clock being at 90°, and on the 21st the mercury at 9 o'clock was 73°, and at 2 o'clock at 80°. Although the lower current of air was south, the

upper

did not seem to follow the same course, but was more from S. of W. This was shown by the course of some electric clouds on the 20th, and of one on the forenoon of the 21st. A little after 2 o'clock on the 21st I observed a large mass of cumulus in the S. E., not at a great distance, and with little apparent elevation. An electric cloud which was passing lay low in the horizon at the S., but between the two there was no connection ; the mass of cumulus was completely isolated, a line of blue sky being distinctly visible between the two; nor was there any appearance of stratus, or the cirri, which invariably accompanies an electric cloud. There was no perceptible wind from any quarter.

I was in my garden some ten or twenty minutes after making the above observations, and not far from 3 o'clock, when my attention was arrested by a heavy roaring in the direction of the cloud, like that which accompanies a fall of hail or violent wind, and looking at the cloud, I perceived that a mass of cirri was streaming from the summit of the mass, and stretching upwards and N. E. from its highest point. There was little appearance of stratus at this time, and not the slightest indication could be discovered that rain or hai] was falling from the cloud. I carefully examined the cloud to detect any motion which might exist in it, but not the least movement was perceptible, except that in a few minutes the stratus began to form rapidly at the base of the cloud, and a visible prolongation and elevation of the cirri was taking place. In a short time rain could be discovered precipitated from the cloud, and the roaring noise continued without interruption, exhibiting a singular contrast to the quiet and immovable state of the cloud. At this time the cloud was about three miles distant, and the angle of elevation shows its height to have been about six hundred feet.

The general movement of the cloud, it was soon apparent, was to the N. W., and in about twenty minutes after the first indications of a shower, I was driven within doors by a fall of the largest

• From Stlliman's American Journal of Science,

drops of rain I think I have ever seen. They were not numerous, but

in falling seemed as large as cherries, and dashed upon the earth with the seeming force of a hailstone. No hail was observed by me, but the size of the drops excited general notice. A heavy shower of perhaps ten minutes followed these drops, but during the whole, though the roaring noise continued unabated, not the slightest wind in any direction could be felt, but the water poured down perpendicularly like a cataract. This was particularly observable when the shower had passed so that the line of fall was about one hundred rods to the west of us. While it was a blue sky over head, at that distance from us, for ten minutes the water was pouring down in a vast sheet, and one mile west of us more water fell than during any other shower of the season. Before the shower had become perpendicular to us, or perhaps twenty minutes after the first rain fell from the cloud, thunder was heard in it; and after it passed, several electric explosions occurred. About five miles to the N. W. it ceased to rain, and the cloud rapidly melted away ; and in two hours from its commencement nothing was to be seen of it except the train of cirri, resembling a streak of white smoke high up the sky.

But the most singular part of this electric shower remains to be noticed. During the time of its passage, on the eastern margin of the cloud, about two miles northeast of us, little rain fell, but hail and snow were both precipitated from the atmosphere. On the west side of the cloud the thermometer was but little affected, not more than is usually the case in summer showers; on the eastern or northeastern side, the cold was perceptible, and the thermometer fell rapidly; but in neither case was their any apparent atmospheric movement to account for such a change. I may remark here, that while the cloud remained stationary just west of us, it was rapidly extended to the south more than a mile, giving a heavy fall of rain to its extreme limit.

I have no particular theory to support or promulgate in giving you the foregoing. One of two things is perfectly clear from the facts as observed by me. The first is, that there was no visible rotary movement in the cloud at any time; and the second is, that there was no rush of surface air to the cloud, which would seem necessary had the noise been occasioned by an internal or central whirl. I have never known a thunder shower in which such a perfect stillness of the whole atmosphere was observable as during the continuance of this. Still some such movement as this seems necessary to account, not only for the noise that attended the cloud, but also for the rapid elongation of the cirri, and the formation of the hail and snow. It would seem that by some ascending movement, the vapour of the cloud and the drops of rain were brought in contact with air below the freezing point; and the large drops of water that fell on the western line of the shower must have been the result of a rapid condensation of vapour by contact with air slightly above that point. Is it not possible that, owing to the different directions of the upper and lower strata of air, a rotary or upward movement may have been produced, drawing into it and elevating the vapour of the upper masses of cloud, the space thus created being filled by more elevated and colder masses, the motion of which to this point would account for the roar, as well as show how the condensation or congelation that took place might have been produced ? In this case the lower air might have remained, as it certainly did, perfectly quiescent, while the upper air was in the greatest agitation.

Parhelia. January 1st was the coldest day we have thus far had this year at this place. The thermometer at 7 o'clock was at — 12°, at 9 o'clock 10°, and at 2 o'clock 4°. It had snowed constantly for about three days, and the average depth was not less than three feet, the wind from the north. On the 2nd, the wind was N. W., the thermometer at nine o'clock at zero, and at 2 o'clock 9° above. At sundown it sunk to 0. A dense haze seemed to hang like a curtain in the west, and a little before sundown, brilliant parhelia were seen, resembling two mock suns. Their appearance when about five degrees above the horizon was somewhat like the following :

Fig. 1.

[graphic]

On Thursday the 16th of January, a day which was generally noted as one of the coldest ever known in this country (the thermometer being at Albany - 26°, at Schoharie 36°, at Utica – 21°, at Syracuse - 14°, at this place — 10°, and at Franconia in New Hampshire 41°), occurred another beautiful spectacle of this kind. When the sun was about a quarter of an hour high the appearance was as below.

Fig. 2.

[graphic]

The colours of the parhelia in this case rivalled the most splendid appearance of the rainbow, and retained them until the sun sunk below the horizon. At that time, what may be called the upper limbs of the parhelia seemed to stand like beautiful columns of coloured light on the base of the horizon.

The next morning, the thermometer being at -6°, the moon, which set at about 6 o'clock, for more than an hour before going down, exhibited the most perfect and splendid paraselene ever witnessed in this place. The appearance was seen in Fig. 3; and was destroyed only by the moon's passing behind a cloud a few moments before setting.

Fig. 3.

[graphic]

To what cause these meteorological phenomena are usually attributed I know not, unless to atmospheric vapour; but in all these cases they seem fairly to owe their origin to the state of the air consequent on the intense cold. The air in such a state of cold is filled with minute crystals of frost, and the reflection from these is perhaps sufficient to account for the general appearance.

But the difference in the figure of these parhelia would seem to prove that this general cause must be subject to many modifications from other agents. Is this change of figure owing to the different forms which it is well known the crystals of snow assume at different times? The explanation I leave with you.

Meteorological Register. Below I have prepared a table of the average temperature, the weather, winds, &c., for the years 1838 and 1839, as observed by me at this place. Otisco is about fifteen miles west of south from Syracuse, and at an elevation of eight or nine hundred feet above that place, on the Senecca branch of the Erie Canal.

Average
Temperature.

Weather, Days. 9, A. M.2, P. M. Clear Cloudy. Rain. Snow. N. IN W. 1838 41 48 162 | 200 | 77 78 18 72 154 66 29 6 2 16 1839 42 51 184 184 | 89 55 (19 66 1351 62 42 26 2310

The extreme range of the thermometer in 1838 was between -8° on the last day of January, and 93° on the last day of July, giving 101°. The range for the year 1839 was — 8°, January 23rd, and 90° on the 30th of July, giving 99o. An instance of those

Year.

Winds and Course.

W.

S. W. S.S.E.E.N.E.

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