the shaking bogs at Bomere Pool, Shropshire. This station, although given some time since by me in this Magazine, on its discovery, has been overlooked by most botanical authors; and, therefore, I now repeat it here. It is in great plenty, but does not always flower freely, and may easily escape notice. Potamogeton zosteræfòlius. In great plenty in a ditch at Baitsbite, near Cambridge.

Eriophorum grácile Sm. In a bog on the top of Dinas Emrys, Caernarvonshire.

Scirpus Savii. Just below the mill on the stream flowing from Llyn Mealog; in a wet place between Newborough and Llanddwyn Abbey; in almost every wet place in Holyhead Island; all in Anglesea. On the ascent of the Hill of Howth, near Dublin. In several parts of Connamara (see p. 129.), and at Kenmare, Kerry. I have a specimen gathered by myself at Caernarvon in 1830, but considered then as S.

setaceus.

Alopecurus fulvus. On the bank of a pond near the Rectory, Copford, Essex.

Agrostis vulgaris var. pumila; synon., A. pùmila Linn. and Lightfoot. On Henfield Common, Sussex, June 18. 1835. I have also found this pretty little plant near Capel Curig, North Wales. It has very much the appearance of a distinct species; but I have not been able to detect satisfactory characters. It may always be known by its fasciculate mode of growth and very small size.

Polypogon monspeliensis. In Canvey Island, near Southend, Essex. June 22. 1835. It grows in a marshy spot, by the road side, between the chapel and some houses on the Thames bank.

Festuca rubra B glauca; synon., F. glaúca [? rùbra] Winch, Bot. Guide, 2. 11. On the sands at Shoreham, Sussex; on the opposite side of the river from the town.

Equisetum hyemale. In the wood at Leixlip Castle, near Dublin.

Woodsia hyperborea. This plant, I fear, is now extinct on Glyder Fawr, Caernarvonshire, as Mr. Borrer and myself (in company with J. Roberts, Esq., of Bangor, a gentleman well acquainted with its exact locality) could not find a single specimen. July 28. 1835.

Edipòdium Griffithiànum. Mr. Borrer and I found this rare moss in crevices of rock, on the upper ledges of Clogwyn y Garnedd, Snowdon. July 25. 1835. It was then nearly over.

[In VI. 367, 368., is published a notice, from Mr. Babington, of localities of Carex speirostachya, Lùzula spicata, and a var. of Festuca ovìna with very hairy corollas deemed probably identical with F. hirsuta Host.]

ART. VI. Some Discussion on the Principles on which Clouds are suspended, with a Recommendation, that those who pursue Meteorology do so cooperatively. By Mr. W. H. WHITE.

As clouds may be reckoned among the most picturesque, pleasing, and useful phenomena of nature, it is somewhat strange that meteorologists have not paid more attention to the contemplation of them, as they, whether rolled into enormous masses, and piled upon each other, exhibiting the shapes of mountains, with summits as white as snow, and valleys, whose openings are distinguished by shades of purple and vermilion (appearances very common in tropical climes *), or viewed in their ever various and lovely characters,

"Where, 'midst the changeful scenery, ever new,
Fancy a thousand wondrous forms descries,
More wildly great than ever pencil drew;
Rocks, torrents, gulfs, and shapes of giant size,

And glittering cliffs on cliffs, and fiery ramparts rise;"
BEATTIE'S Minstrel.

are fit subjects for philosophical investigation, and must be admired, by every contemplative mind, for their beauty, and for their endless combinations. What is now luminous will, in a few moments, become coloured; what is coloured will soon mingle into shade; or form the most beautiful and picturesque representations of islands, towns, bridges, arches, ruins, huge rocks, and gigantic mountains.

If, then, clouds are subjects of such great interest, an enquiry into the cause of their suspension in the atmosphere, I consider, will not be uninteresting to your meteorological readers; especially if the few ideas I shall advance should lead to further and more satisfactory enquiries on the subject: for I consider this department of meteorological science to be greatly neglected. This subject has engaged my attention for some time past. I have sought for an explanation of this beautiful phenomenon among the works of our best meteorologists; but I have found nothing satisfactory. The conjectures (for all the opinions I have met with, in the course of my reading on this subject, are mere conjectures) I have seen thrown out on the subject are not only very crude, but very

[* A remark by the late Rev. Lansdown Guilding relative to a notice in II. 297. In a bright tropical sunset, the sun's rays will often tinge with green a considerable portion of the west, This unusual colour, associated with violet and golden hues, adds much to the gorgeous splendour of a scene which nothing earthly can equal.-L. Guilding. St. Vincent, May 1. 1830.]

far from being any thing approaching to a solution of the enquiry, How are clouds suspended? I will just mention one or two of those conjectures before I offer my own remarks. De Luc supposes that each particle of the vesicular vapour which constitutes clouds contains a small portion of hydrogen gas; and this gas, he says, enables the particles, like so many little air-balloons, to remain suspended in the atmosphere at different elevations. This same naturalist also conceives, not proves, that this hydrogen gas is derived from a supposed decomposition of a portion of the water itself. He, therefore, gives no explanation of the cause, or proof of the effect. Now, it appears to me, and I think it will appear plain to every careful observer of nature, that, if this theory of De Luc had been founded on actual observation, the presence of this hydrogen gas would have been detected, either on the summits of "cloudcapt" mountains, or, indeed, in any other place in a foggy atmosphere; but I am not aware of any meteorologist ever yet having made such a discovery.

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I have perused the theory of Mr. Luke Howard on this portion of meteorology with no better success. Howard supposes each particle of vesicular vapour to be " similarly electrified," and that, consequently, they "repel each other." Now, admitting this repelling property to retard condensation, which it would have a tendency to do, it would not prevent the descent of the vesicles; for each globule of water, how minute soever it might be, would be heavier than the circumambient air, and, consequently, would, by the force of gravity, fall to the earth, although with a less velocity than a considerable volume of the same fluid. I, therefore, do not consider the suspension of clouds to be at all accounted for by either of these hypotheses; nor do I know of any other that claims superior attention.

How distinguished soever for learning and science may have been our predecessors, we are not bound to show them deference, by blindly embracing their opinions; for the very spirit which carried them to a certain extent of knowledge in their days would, could they revisit this

"Poor pitiable speck our earth,"

and renew their studies under all the advantages which they themselves so ably contributed to produce, carry them onward to greater improvements, and to the rejection of many erroneous opinions they formerly entertained. We live in a world surrounded by objects of high interest, whose influence has great effect on our existence and comfort, and whose varied impressions strike our senses with wonder and astonishment.

And yet, the more we contemplate the works of nature, the more we are impressed with our own insignificance, and the greatness of the Almighty Creator; and the longer we live, the more we shall find we have to learn; for

""Tis but a part we see, and not the whole."

In order to ascertain the principle of the suspension of clouds, particular attention will be necessary both to the temperature and density of the atmosphere, as the quantity of moisture it is capable of dissolving greatly depends upon these circumstances. A much larger portion of aqueous vapour, it must be recollected, is held in an elastic form near the surface of the earth, than in the more elevated regions of the clouds. In high regions, even on the summits of high mountains, atmospheric pressure opposes very little check to the natural tendency of water to assume an aeriform state; consequently, the higher we ascend in the atmosphere, the quantity of moisture which is held in solution goes on diminishing, until we arrive at the precise altitude beyond which the effect of diminished pressure predominates, and the aqueous vapour goes on increasing, according to Professor Leslie's Relations of Heat and Moisture. This is, then, that medium point in the atmosphere which clouds occupy, and above which they rarely ascend, at least so far as my observations go; and I am led to this conclusion by that beautiful provision made by nature for preserving a constant circulation in the atmosphere by causing every accession of heat to be invariably accompanied by a corresponding decrease in density. Supposing, then, an ascending column of air to have reached that particular height at which its diminished temperature no longer allows of its retaining the whole quantity of moisture it had dissolved near the surface of the earth: it follows, that a portion of water becomes disengaged in that state which is termed by meteorologists vesicular vapour; that is, as I understand it, vapour holding intermixed with it some portion of atmospheric air; hence it appears, that, as the air is considerably more rare about the usual elevation of the clouds (from two to three miles), it not unfrequently occurs, that the watery globules in their descent meet with a stratum of air of that density which is just equivalent to the weight of the vesicular vapour and the contained atmospheric air together. At this point they will remain suspended, till such time as the air contained within the different vesicles becomes of equal density with the surrounding atmosphere; when the particles will coalesce, and form larger drops, and, consequently, become too heavy for the atmosphere to support; and, hence, they

will descend in the form of rain. I think I am borne out in this opinion by the well-known fact, that hailstones, which are evidently derived from the same source, are usually found to be hollow in the centre; and, also, that the low specific gravity of large flakes of snow, which descend so slowly and majestically through the atmosphere, is to be attributed to the same cause. Taking the term vesicular vapour in its common acceptation, as applied to the moisture of clouds and fogs, it seems scarcely possible to conceive any disengagement of moisture to take place, without, at the same time, supposing a certain portion of air to be intermixed with it.

I will now endeavour to put this theory to the test, by applying it to one or two of the principal modifications of clouds, as laid down in Howard's nomenclature. And, first, the cirrus, or that species of cloud which has the greatest variety of extent and direction; sometimes remaining almost stationary for many hours, and at other times undergoing exceedingly rapid changes; so that the cirrus cloud has been denominated the "Proteus of the skies." After some continuance of clear weather, the cirrus is frequently the first cloud to be seen; appearing like fine white threads, penciled, as Mr. Howard has it, on the clear blue sky. These fine threadlike pencilings, if I may so denominate them, occupy the highest station in the atmosphere; and are, I conceive, immediately formed from the setting free of the vesicular vapour; and, hence, they occupy that precise line of elevation at which the quantity of moisture held in an aeriform state is at its minimum. They therefore often remain, in the summer time, for a long time without having any apparent increase or diminution; because, while the evaporation is continually going on from the upper surface, and thereby tending to diminish the clouds, the ascending portions of air keep continually supplying on the lower surface, so that no actual diminution takes place; but, when the ascending portions exceed the evaporation from the upper surface, then the clouds begin to descend, or gravitate slowly towards the earth, and, at the same time, proportionably increasing their bulk; and thus form, in the second place, that modification of cloud, which Howard terms cumulus *; which, also, will be found to occupy that particular line of elevation at which the density of the atmosphere is exactly equivalent, as in the former case, to the weight of the vesicular vapour, containing portions of atmospheric air mixed with it.

I do not submit these observations to your scientific readers *It is very interesting to witness the inosculation of different modifications of clouds.