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sudden changes which occur in our climate, took place on the 19th of October, 1839, when the wind, which during the fore part of the day had been S. W., at half-past 2 o'clock suddenly veered to N. W., and the thermometer fell from 650 to 24° in three and a half hours; a difference of 41 degrees.

I have for several years noticed the fact, that whatever may be the direction or course of the lower strata of clouds, that of the cirri, or highest of all clouds, is almost invariably from west to east. It is nothing uncommon to see the lower clouds drifting in heavy masses, and with a strong wind to the N. or N. E., while far above them, the streamers of the cirri are floating undisturbed towards the S. E. or E. Indeed it is very rarely observed that cirri take any other course, and it may fairly be inferred they never do, until by greater condensation they approach the nature of cumulus, and sink into the action and influence of the lower currents. From their observations on these clouds on the Cordilleras of South America and Mexico, Humboldt and Boussingault have inferred, and I think with good reason, that in the upper regions of the atmosphere there is a current constantly flowing from west to east, an inference which, if admitted, assists materially in developing the theory of storms, sudden changes of temperature, &c.

A glance at that part of the table showing the course of the wind will explain the fact noticed by Darby and others, that the mass of trees growing on the eastern shore of the great lakes have a sensible inclination to the east, and that in all cases where the hemlock occurs, the long, flexible, terminal twig of that tree has the same uniform declination from the perpendicular, and in the same direction, a little north of east. The same thing may be observed of orchards, in which probably nine tenths of the trees in exposed situations have a similar inclination. In the first year, two hundred and twenty days of the three hundred and sixty-five the winds were from the W. and S. W., and in the last one hundred and ninetyseven. The remaining days the winds were so equally divided as not to counteract this influence in the least, and consequently the winds from that quarter overpower all others.

The average temperature of the years 1838, 1839, and 1840, for the months of January and February, is given below.

January

February 1838

26° 1839

20° 1840

14° Time of observation, 9 o'clock, A. M.

Thus, it seems January of this year averages 12° colder than 1838, and February of this year 17° warmer than that year.

The month of April with us has been remarkable for its extreme and rapid fluctuations. The warmest day recorded of any April here, was on the 25th. On that day the thermometer in the shade

9° 24° 26°

at 2 P.M., was at 85°, and at 3 P.M., 86 ; on the 27th at 6 A.M., it stood at 28°; being a change of 58° in 37 hours. On the 18th at noon the thermometer was at 80°; on the 19th at sunrise, it was at 29° ; being a change of 51° in 18 hours. The range of the thermometer from Jan. 1st, when it was - 14°, to April 25th, when it was +86°, is 100°; a difference rarely equalled in our changeable climate.

A Description of a Halo or Corona of great Splendour, observed at

Greensburgh, Westmoreland County, Pa. By ALFRED T. KING, M. D.

If you consider the subjoined description of one of those meteorological phenomena, usually denominated by philosophers coronas or halos, which was observed in this town about eleven o'clock A.M., on the 28th of August last, and which excited considerable interest among the intelligent portion of the community, and apprehension and alarm in the minds of the uninformed, worthy of a place in your excellent journal, it is much at your service.

[graphic]

This phenomenon consisted of from three to five circular belts or zones of light, one of which emulated, in appearance, the splendor and magnificence of the most gorgeous rainbow. The arrangement : of these rings are somewhat singular; the first, or inner one, which had the sun for its centre, was truly brilliant, exhibiting all the prismatic hues of the rainbow, the colours of which were so dazzling that the unprotected eye could scarcely rest upon it a moment. This, I presume, was occasioned by the sun being near the meridian, and consequently many of his rays would impinge upon the halo, without passing through the mass of vapour, to the existence of which

• From Silliman's American Journal of Science.

scene.

I attributed the formation of the halo. The outer circles, however, one only of which appeared to be perfect, were composed of pure white light, and had for their centres the circumferences, or a point near it, of the inner ring. Consequently, these circumferences, if all the circles had been perfect, would necessarily have passed through the apparent situation of the sun. I mentioned, however, that only one of these rings was perfect, the others were concentric arcs of circles which crossed one another, as seen in the accompanying diagram.

In the centre of the inner circle and bounded by it, a bluish mass of dense vapour was perceptible, which gave to the whole an embossed appearance, and added much to the beauty and brilliancy of the

Around and within the exterior circles there were also perceptible masses of vapour, though obviously much less dense than the mass which was nearer the sun. With the exception of these masses of vapour, and a large cumulus which lay to the south of us, and here and there a few scattered cirri, the sky was cloudless and the atmosphere calm and serene. The mercury in the thermometer stood at 86o. The weather continued thus for thirty-six hours, when we had a smart fall of rain, and a descent of the mercury in the thermometer to 36°, at which point or near this, it has remained until about three days since, when it rose to 66o.

Coronas and parhelia have frequently been observed and accurately and glowingly described by many scientific gentlemen, and various and conflicting opinions have been entertained respecting their causes; some attributing them to the peculiar state of the air consequent upon intense cold, while others, probably more correctly, attribute them to the refraction and reflection of the rays of light through masses of vapour which are formed in such aggregations as are not heavy enough to fall in the form of drops.' Descartes remarks, that halos never appear when it rains. Coronas have frequently been observed around the moon, and even around Sirius and Jupiter, but, as far as my information extends, they have been but seldom variegated, even when they have encircled the sun.

I know not to what cause this phenomenon can be attributed, unless it be to the refraction and reflection of the sun's rays through the masses of vapour. Doubtless the first circle was thus formed, and if we suppose the rays of light from the circumference of this circle to be again refracted and reflected through another mass of vapour, an outer ring would evidently result. Again, if we suppose the same to take place from another point of this circle, a second ring would be formed which would cross the other in some point of its circumference, and in like manner, I presume, any number of rings may be formed. I offer this explanation, however, with much diffidence.

On the Variable Action of the Electric Column.

By Mr. J. A. DE Luc.*

(Continued from page 243). Sir,- Your number of June last contains a paper of Mr. Ronalds's, which could not but interest me, as it relates to the variable action of the electric column. This variableness depends on many causes, with respect to one of which we do not agree, and it will be the object of this paper.

I have found in my experiments, that an increase of moisture did increase the action of the column. Mr. Ronalds is of a different opinion; but as he describes the experiments from which he concludes that moisture has a very little effect on that action, it will be easy for me to show that this disagreement between us results from a mistake on his part, and that his experiments, though very ingenious, according to his idea of the subject, are quite dissimilar to those whence I had derived

my conclusion. One single circumstance will show that Mr. Ronalds did not understand my meaning. I could not refer but to the column which I had described, of which an essential circumstance is, that it is in communication with the outside air, and thus influenced by its degree of moisture ; whereas Mr. Ronalds's experiments have been made with one of Mr. Singer's columns of 1000 groups inclosed in a glass tube : that tube therefore precluding the action of the external air, the inclosed column cannot be affected by its changing degree of moisture. I do not doubt that when Mr. Ronalds shall consider that difference between our experiments, he will judge that the results which he relates in his paper, though interesting in themselves, cannot be opposed to mine : but I must come to particulars, because they will contribute to a further explanation of this new physical apparatus.

The action of Mr. Ronalds's column was indicated by the number, in a given time, of the strikings of the gold leaves in an electrometer: in his second experiment made under a glass receiver, the strikings having been five in the beginning, while the hygrometer was 41°, and the thermometer 532, the strikings were reduced to three, when the hygrometer ascended to 41), and the thermometer descended to 53° : which experiment appears to favour Mr. Ronald's idea, that the increase of moisture rather lessens than increases the action of the column. But in this experiment the column being inclosed in the glass tube, the increase of moisture took place on the surface of the latter, which produced an increase of conductive faculty for the electric fluid on that surface, which lessening the difference of electric state of its extremities, diminished consequently its effect on the electrometer.

The third experiment, in which the room was gradually heated, shows a case in which I had partly made a mistake, pointed out to

• From Tilloch's Philosophical Magazine.

me by Mr. Singer. In one of my experiments, when the sun-rayg fell on my column the number of strikings sensibly increased, and returned gradually to their former number when the sun-rays ceased to fall on it: this effect I attributed entirely to the action of the sun-rays themselves; but Mr. Singer conceived that it was only the effect of heat thus increased in the column. I considered this explanation as deserving to be submitted to direct experiments; I have since long observed the column under this point of view, and found that the increase of heat had a great influence to increase the number of strikings. But this is not an effect so simple as I thought it at first; for, with the same increase of heat, I have found great differences in the increase of the correspondent number of strikings; which circumstance I continue to think must be owing to the difference in the electrical state of the ambient air; and thus the column is, as I had found it in my first observations, an aërial electroscope, which property Mr. Ronalds had also surmised. But too many causes interfere with that state of the ambient air, to distinguish that effect with certainty; and it will require a longer study of the variation of the effects by different circumstances, in order to assign the true influence of each of them.

Mr. Ronalds's experiment 7 is a confirmation of those which I had described in a paper published in the Philosophical Transactions of the Royal Society for 1791. These experiments were made in order to show the cause of a dissentiment between M. de Saussure and myself on the point of extreme moisture, which I had prescribed to be taken in water itself; the reason of which I stated in my first paper on the hygrometer, published in the Philosophical Transactions for 1774. The construction of M. de Saussure's hygrometer did not permit to dip it in water, because the index was in the lower part of the frame, and the hair of which it is formed could not be dipped in water without the whole instrument, its index and scale, being immersed into water : he therefore fixed its point of extreme moisture under a receiver inverted on a dish full of water.

Unluckily this circumstance did not permit M. de Saussure to discover the defect of the hair and of all the threads of fibrous substances, which is to relent successively their lengthening when moisture increases, and even at last to grow shorter, more or less according to their nature, when moisture approaches to its extreme; which circumstance excludes all the threads from a true hygrometer. But my hygrometer, consisting of a slip of whalebone cut across the fibres, is not subject to that defect; it lengthens up to the point of extreme moisture taken in water, and with it I made the same experiment under the receiver inverted on water; and thus I found the important law of hygrology, that the utmost quantity of evaporated water under such a receiver does not produce extreme moisture in the enclosed space when the degree of heat is sensibly above 32 : and that it recedes from it in proportion as the heat increases. Mr. Ronalds has found the same effect in his experiment 7; for as long as the temperature was 55, which lasted a

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