When water is dissolved in air, it constitutes, together with it, a fluid perfectly transparent, all refractive power of the water, whatever it may be, upon whatever it may depend, ceasing. When separated from this state of solution, by the aggregation, from whatever cause, of the dissolved particles, their first action upon light passing through them, are of inflection by the air in which they float adjacent to each. By further accession of particles, globules are constituted, through which the light passes, and in passing in and out, is subject to the ordinary reflections and refractions of transparent bodies, by refractive powers, beginning at smaller sizes, and increasing as those increase, up to the ordinary refractive power of large masses of water in air. This gradual acquirement and increase of refractive powers obviously follows from the phænomena of thin plates of water in air, or of air between glass. In the case of a bubble of water in air, when the tenuity of the film at the top is extreme, it ceases altogether to act in that part on the light, which passes through, as if no body was interposed between the parts of air; at increasing distances from the top, the tenuity of the film increases, but not sufficiently to possess any refractive or reflective powers; the light arriving in the water between the parts of air adjacent to the water, is inflected by the air into two portions, one of which passes on, the other returns; and these inflections are continued and varied in orders, dimensions, and colours, until at last at increased distances and adequate thicknesses they cease, and the ordinary reflections and refractions are restored to the water at both surfaces of the film. As this is effected, gradatim not per saltum, these powers beginning and increasing pass through different states of intensity, from evanescence to their ordinary state. The same is the case of air between two plates of glass, and the evanescence, restoration, and gradual increase of the refractive powers of transparent fluids, in these and similar circumstances, is thus fairly established, together with every principle necessary to the formation of this iris.

These globules may occasionally be so formed and arranged into striæ of various directions, as at once

to exhibit, by their refractions through the drops, the iris of forty-five degrees, with its coloured mock-suns, and by reflections at the surfaces of the drops arranged in longitudinal striæ, the white almicantars with white suns in them so rarely seen. By a small portion of unguent spread over the surface of a looking-glass, and disposed into various striæ of various directions by rubbing, strong resemblances of these white atmospheric lines extended to considerable lengths, and variously crossing each other, may be exhibited by the reflected light of a candle. If, therefore, this whole course of reasoning can be maintained, the whole theory of these atmospheric phænomena may be considered as established, by referring their formation from the number and parallelism of certain rays to the principles of formation of images by radiants, and from icy machinery of doubtful existence and application to globules of water, to floating globules, dependent for their floatage and diminished refractive power on the same cause, and to falling drops of fully-restored refractive powers.

I offer, not without due consideration, this explanation of these phænomena, certainly better, and better founded in its principles than all which have preceded, than the prismatic stars of ice of Des Cartes, and the snowy kernels and cylinders of Huygens, and certainly more consistent with circumstances, and the general order of things. I see distinctly in the globule or globular circle, the elements of the iris. I observe dimensions in the iris which require a refractive power in the drops different from that of water, in other its usual states of aggregation. I establish from other phænomena an adequate change of refractive power in the drops of the vapour; and to him who would reject these facts and their consequences, I would offer the propositions themselves and the conclusion, in the simple form of queries, after the example of Newton. They may, at least, be fairly enumerated conjecturally among observations on the causes and phænomena of the floatage of small heavy bodies in the atmosphere.

ART. IX. A Letter relating to Mr. Watts' Remarks on Captain Kater's Experiments, &c., addressed to the Editor of the Quarterly Journal.

SIR,

I AM tempted to give you the outline of an article in the second Number of the Edinburgh Philosophical Journal, by a Mr. William Watts, of the Custom-house, Penzance, entitled, "Remarks on Captain Kater's paper, containing experiments for determining the length of the seconds pendulum in the latitude of London."

The writer begins by mistaking the length of the seconds pendulum for that of the pendulum of experiment; and in consequence arrives at the conclusion, that the number by which the square of the arc of vibration is to be multiplied" is incorrect,” and should have been 1,645 instead of 1,635, the number given by Captain Kater.

He next convicts Captain Kater of not having expressed the number of vibrations made by the pendulum in 24 hours, beyond the nearest hundredth of a vibration.

He then proceeds to point out, that Captain Kater has committed an error in his computation of the correction for the buoyancy of the atmosphere in one of the 12 series of experiments, to the amount of two hundred thousandths of an inch. This being divided by 12, might occasion an error of about two millionths of an inch, in the length of the pendulum vibrating seconds. And lastly,

He asks," why cannot the disappearance of the disk" (in the observations of coincidences), "be noted to a quarter of a second, as readily as an entire second;" or, in other words, why cannot an object be seen through a telescope when it is not in the field of view?

October, 1819.

I am, Sir,

Your obedient Servant,

and constant Reader,

Z.

260

ART. X. Journal of a trip from St. Thome de Angostura, in Spanish Guayana, to the Capuchin Missions of the Caroni.

[The following Journal is printed from the original Manuscript, for which the Editor is obliged to a near relation of the Author.]

October 29th, 1818.

HAVING agreed with Dr. K. to accompany me, and purchased a horse for 20 dollars, a mule for 45 dollars, and received another as a present from Bolivar, we started at 4 P.M.; our equipage consisted of myself upon a cream-coloured horse, the Doctor upon my little mule, each armed with a broad sword and a brace of pistols in our holsters; my boy John upon one mule, and my guide Anisette upon another, each armed with a rifle and sword, drove before them the baggage-mule, loaded with two portmanteaus and a bag containing biscuit, sausages, and one day's provision, with six bottles of good rum, salt, pepper, and other needful articles which we were given to understand were not to be had in the interior. Our intention was to go no further than Panapana, about six leagues' distance, where we expected to find the Doctor's cavalry. The day had been cloudy and cool, but without rain; our path lay on an elevated plain, skirting the banks of the Orinoco, which ever and anon shewed itself, rolling majestically along in the distance. I wished to push on, but could not get the baggage out of the ordinary mule's pace; and, being unable to distinguish my road among the innumerable cattle paths which crossed us in every direction, was e'en obliged to content myself with a most uneasy jog trot. The country around Angostura is an elevated savannah, mostly covered with wiry grass and stunted trees, affording little shade. Looking southward, the land appears to rise; and from several points we could see a distant range of hills apparently clothed with wood. Occasionally occur the beds of torrents, in which the soil is rich and wooded; but in most places it yields barely sufficient for pasturing the mules and cattle, that are driven from the interior for the use of the capital. At about 11 leagues' distance, crossed a small stream called the Cano-fistula, and 11 league further another called the Marnanta,

whose sandy bed and deep channel shewed the sterility of the elevated surface, and the immense body of water it sometimes pours into the Orinoco. On the right bank stood a small village of the same name, once containing probably three or four hundred inhabitants; but the mouldering habitations, and gardens overrun with bush, attest its present complete abandonment. We had hitherto passed but one hut on our way; and the desolate aspect of the place gave us no favourable impression of this portion of Guayana. The sun was already going down, and we had three long leagues of nearly four miles each between us and Panapana. Jogged on, and just before dark, passed the rapid torrent Candelaria, then tolerably dry: had much rain fallen, we might have been detained some hours; but its vicinity to the Orinoco, prevents its continuing full long together. Groped our way onwards in the dark, scrambling over the stones in an unknown and scarcely perceptible track; but our beasts were fortunately more used to this work than their riders. At length half a mile of wood brought us to the banks of the Guaynare, which we knew to be near the end of our ride. But our difficulties were not yet over. The descent was steep; the water pretty deep, and my horse expecting to swim for it refused to advance, until I should a Llanero, dismount, take the saddle on my head and shew him the way. With much. flogging and spurring, however, at last in we all plunged together, and reached the other side with no other injury than the wet; but it was between eight and nine ere we arrived at Panapana. The Commandant, Gaspar Uraca, unused to such late visitors, and just going to supper, turned out in alarm with spear and shield to receive us; but being answered in the usual tone of salutation, desired us to alight, and ushered us into his abode. We took up our quarters, i. e., slung our hammocks over his counter, for his was the only shop we met with in the district. The village is conveniently situated, about half a league from the Orinoco; it once contained several Indian families; and, in the time of the Spaniards, actually furnished 100 men to the militia; but the war and the fever had made such havoc, that 48 Indians were the whole that remained; and these, with a few cavalry and Creoles, formed the whole population. The barren