of caloric which must hence be liberated; from this he subtracts the heat necessary to carry off the matter of perspiration, and thus finds the quantity of caloric which is employed in raising the temperature of the body. He procured a weight of water equal to that of the body, and after raising it to 98, he observed what quantity of boiling water was necessary to keep it at this temperature, in the medium state of the atmosphere; this he observed to be much greater than the heat resulting from the chemical effects of respiration.

Upon this, which we believe to be a fair statement of the argument, we shall remark, that it is not denied by Mr. Wilkinson, that a considerable quantity of heat is liberated by respiration, but that the quantity is supposed to be insufficient. The controversy is thus reduced to a question of degrees,and the strength of the argument must depend upon the accuracy of the data.

The quantity of oxygene consumed is deduced from the experiments of Mr. Davy alone, while those of Dr. Menzies and M. Lavoisier are not noticed. Now it must be observed that the object of the former of these physiologists was principally to discover the nature of the change produced upon the air, whereas that of the two latter was immediately directed to ascertain the absolute amount of this change. In the present investigation therefore, their experiments were more in point than those of Mr. Davy, and it will be found upon examination that their estimates of the quantity of oxygene consumed is greater than that assigned by our author,

The amount of the perspirable matter is deduced from the experiments of Sanc. torius, Bryan, Robinson, and Hales. However ingenious their deductions might appear, at the time when they were published, we conceive, that in a question like the present, the resolution of which depends altogether upon the accuracy of numbers, little regard can be paid to them. It is generally admitted, that the perspirable matter was much over-rated by these physiologists, in consequence of their not being aware that the weight of the air expired, exceeds that of the air taken into the lungs. Lastly, it may be remarked, with respect to Mr. Wilkinson's comparative experiment, that the water would, for obvious reasons, be cooled more rapidly than an animal body of the same bulk and the same temperature.

Admitting, however, that our author had overthrown the chemical theory of respiration, let us examine the arguments which he employs to establish his galvanic hypothesis. They are not very distinctly stated, and appear rather in the form of assertions, than posi tions deduced from fact or analogy. The similarity between the structure and mechanism of the lungs, and elec trical organ of the torpedo appear to be the principal support of his doctrine. The peculiar apparatus of the torpedo consists of a number of rec. tilinear and parallel cells, of equal diameter through their whole extent, not communicating with the external air, or with each other, divided by a number of transvese partitions, filled with a mucous fluid, and furnished with an extraordinary proportion of nervous matter. The cells of the lungs are of an irregular shape and arrangement, branching out from the main trunks into smaller and smaller cavities, all communicating with the main trunks, and these with the open air; they are of course always filled with air, are free from interruption from their commencement to their termination, and are remarkable for the small number and minute size of their nerves. Add to this, that the torpedo, besides this peculiar organ, has a distinct apparatus for respiration, and that no sensation or action, in the least degree resembling the elec tric shock, was ever produced by the lungs of any animal.

Our readers will probably by this time, have formed a tolerably accurate idea of the merits of Mr. Wilkinson's performance. With respect to his dili gence in the collection of materials, there is not much cause for complaint, though, even on this score, we could point out some deficiencies. But we fear that the impartiality of just criticism will not allow us to extend our commendation. The most important facts, and the most trifling conjectures are stated with equal minuteness. Speculations which, in the infancy of the science, were perhaps entitled to the equivocal praise of inge nuity, but which later discoveries have completely discarded, are set forth with wearisome prolixity. Instead of stating in a few words the general outline of an hypothesis, or of a set of experiments, we have long quotations of many pages, taken verbatim from the different au thors. A striking defect in a work of this kind, is the almost total absence of

moving these obstacles. He has at tempted to define the leading varieties which the clouds assume, and to establish a nomenclature descriptive of these different modifications, by which means observations may be more easily made, and more accurately recorded. He has followed the plan pursued in the other branches of natural philosophy, of adopting terms derived from the dead Fanguages, though instead of founding them upon the Greek, as is generally the case, he has employed names taken from the Latin His reason for this deviation from general usage, viz. that the terms would be more intelligible, we think a good one for not using those of Greek derivation; but we are farther of opinion, that the same reason ought to have induced the author to use plain English names in a science, the farther improvement of which will, probably, in a considerable degree, depend upon the observations of the unlearned.

He assumes, as the basis of his arrangement, three simple and distinct modifications; these, however, may be connected together, and pass into each other, thus producing intermediate forms. The simple modifications are thus named and defined.

"E. Cirrus. Def. Nubes cirrata, tenuissina, quæ undique crescat.

"Parallel, flexuous, or diverging fibres, extensible in any or in all directions.

"2. Cumalus. Def. Nabes cumulata, densa, sursum crescens.

“Convex or conical heaps, increasing upward from a horizontal base.

"3. Stratus. Def. Nubes strata, aquæ modo expansa, deorsum crescens.

"A widely extended, continuous, horizontal sheet, increasing from below.

"The intermediate modifications which require to be noticed are;

4. Cirro-cumulus. Def Nnbeculæ densiores subrotundæ et quasi in agmine appositæ.

Small, well defined roundish masses, in close horizontal arrangement.

"5. Cirro-stratus. Def. Nubes extenuata

sub-concava vel undulata. Nubecula hujus modi apposita.

"Horizontal or slightly inclined masses, attenuated towards a part or the whole of their circumference, bent downward, or undulated, separate, or in groups consisting of small clouds having these characters.

The compound modifications are : “6. Cumulo-stratus. Def. Nubes densa, basim planam undique supercrescens, vel eujns moles longinqua videtur partim plana

partim cumulata.

"The cirro-stratus blended with the cu mulus, and either appearing intermixed with

The rain cloud. A cloud or system of clouds from which rain is falling. It is a horizontal sheet, above which the cirrus spreads, while the cumulus enters it laterally and from beneath "

Every attentive observer of the visible appearance of the heavens must have frequently noticed phenomena similar to those above described. The definitions given of them seem, upon the whole, correct and appropriate. We think it, however, in some degree doubtful, how far all the modifications which are enumerated, can strictly be comprehended under the term of clouds. We shall propose the following defini tion of a cloud, which we apprehend will embrace both the popular and scientific idea usually attached to the word. A cloud is a quantity of water suspended in the atmosphere, assuming a visible form, and a definite shape. If it be admitted to be correct, some of the modifications of the stratus, as where it is said to consist of a mist creeping along the surface of the ground, will be obviously excluded by this definition. It may also be questioned, how far the author is correct in considering the cirro-strato-cit mulus, or nimbus, as a distinct modification. Even allowing that rain is produced from the cause assigned by Mr. Howard, and that it is always produced from the same cause, positions which we are inclined to controvert, we conceive that the alteration which the appearance of a cloud assumes when it begins to discharge rain depends upon the presence of the drops of water which, ceasing to exist as component parts of the cloud, are descending towards the earth.

merated by Mr. Howard by no means We also think that the species enu include the whole even of the more important modifications which clouds as sume. Without attempting to fill up the deficiency, we shall mention two, which we are frequently in the habit of observing, and which we cannot arrange under any of Mr. Howard's definitions. The first is a system of long strips, and spreading towards the zenith, like diverging from a centre in the horizon, the meridional lines on a globe. The other is an appearance of the clouds very similar to that of milk when beginning to undergo the process of coagulation; in

some parts of England it has obtained the appropriate name of a curdled sky. The author proceeds to examine each of the modifications a little more at large, and to speculate upon the mode of their formation, and their action upon each other. In this part of his work he exhibits marks of accurate observation, and displays considerable ingenuity in the connexion of his facts, and their application to the general principles of meteorology.

His speculations on the formation of the nimbus, or rain cloud, are the most novel. Before rain can fall, he supposes that a specific arrangement of the clouds must take place; however heavy and numerous they may appear, no water can otherwise be discharged from them. The hypothesis is that there must be two distinct layers, one above, consisting of a thin sheet or light veil of haze, below which the heavy rounded clouds are driven by the wind, or originally formed; the contact, or even proximity of these two sets of clouds causes the rain to descend.

We feel a degree of difficulty in attempting to controvert an hypothesis, which, like the present, is advanced as little more than a mere statement of a matter of fact. Were we to assert, that we have frequently watched the commencement of rain without noticing the appearances mentioned by the author, the reader would probably be as much disposed to accuse us of negligence, as Mr. Howard of inaccuracy. We shall therefore adduce a train of circumstances, the existence of which we think will not be disputed, that appear to us totally repugnant to the theory advanced above. In that peculiar state of our atmosphere, which attends a S. W. wind in winter and spring, the early part of the morning is frequently pleasant; the sky has a few light clouds scattered over it, and persons inexperienced in meteorology, are tempted to predict the continuance of fine weather. In the course of the forenoon, however, the breeze increases, irregular broken clouds appear in the horizon, and are borne along by the wind near the surface of the earth. These increase, until at length they begin to discharge their contents, either in the form of squally showers, or of heavy continued rain. During this process we may observe the higher clouds nearly at rest, retaining the rounded form, and apparently floating in a serene atmo

sphere. Hence it seems that the upper stratum of air, which is not under the influence of the $. W. wind, has a tendency to retain the water of its clouds, while the breeze itself is loaded with clouds in an opposite state, strongly disposed to discharge their contents. These effects, we conceive, are not produced by the action of the different clouds upon each other, because those in the upper stratum retain their figure and situation, and do not appear in any degree to participate in the changes which take place below them.

As it is agreed on all hands, that clouds primarily depend upon the evaporation of water from the surface of the earth, the nature of this process naturally becomes an object of attention to the meteorologist. The theory of the solution of water in the atmosphere by chemical affinity, and the modification of this hypothesis proposed by Dr. Hutton, are referred to, but both considered as inapplicable to explain the phenomena. That which our author adopts is the one proposed by Mr. Dalton, originally stated in the last volume of the Memoirs of the Manchester Society, and which has been so fully developed in the late numbers of Nicholson's Journal. Proceeding on this hypothesis, our author lays down a series of propo sitions respecting the nature of aqueous vapour. He conceives that it is immediately produced by the union of water and caloric; its formation is regulated by the temperature of the water, the quantity of surface exposed, and the vapour already existing in the atmosphere. The vapour, when formed, diffuses itself by its own elasticity; the warmer is the air, the more vapour can subsist in it. When a cold body is presented to the atmosphere, the vapour is decomposed, its caloric is attracted by the body, while the water is deposited upon its surface. The formation of clouds is, in the same way, supposed to be the consequence of the decomposition of vapour; the caloric entering into the neighbouring gases, while the water is precipitated.

The production of dew, which is nearly allied to that of clouds, has been frequently explained. During the heat of the day, vapour is carried up from the surface of the earth into the air; when, in consequence of the absence of the sun, the air becomes cooled, the vapour is decomposed and descends in the form

of dew. As the most simple species of cloud, and the one most resembling dew, the formation of the stratus is first explained. When the dew is deposited upon a surface warmer than the atmosphere, it will be again in part evaporated, and water will continue to be evaporated from the earth, so long as the temperature of the surface remains above the point which counterbalances the pressure of the incumbent aqueous atmosphere. Consequently when the earth has been much heated in the day, there will still be evaporation during the night; an occurrence which, for obvious reasons, will take place to the greatest extent during the autumn. This vapour, how ever, is soon condensed, and of course begins to descend, when meeting the ascending vapour, it condenses part of it, and, by the union of the two, drops are produced, which take the form of the

stratus.

be

We conceive that most of our readers will agree with us in thinking the above hypothesis confused and intricate. While the surface of the earth continues warmer than the superincumbent air, evaporation will continue, and we conceive it possible that part of the vapour may deposited and again evaporated, but still we do not perceive how any thing but dew can be produced. By the continuance of this process, the vapour will be come more and more condensed, until the whole of it is converted into dew, and finally deposited on the earth.

In order to explain the formation of the cumulus, the author observes, that when the air becomes warmed by the sun's rays, the vapour produced does not as before become condensed near the surface of the earth, but is carried up into the higher regions of the atmosphere before it parts with its caloric. There is, however, a certain elevation, at which this process must take place, where the cumulus will be formed. We are here naturally led to inquire, why this peculiar species of cloud always assumes the rounded form. This peculiarity in its outline is attributed by the author to the agency of electricity. We have many well established facts, which may be said to prove that clouds are generally in a state of considerable electrization, and Mr. Howard conceives that the small particles of water, of which they are composed, will, from this cause, arrange themselves into regular spherical

Trasses.

important agency of the electric fluid in the formation of clouds, and we are much disposed to agree with the author in his application of it to the present case. Yet we confess that we are not altogether satisfied with the explanation of the cumulus. If we are not much mistaken, this species of cloud is the most frequently seen, when the air is cold, particularly when the wind comes from a N. or E. point; and a circumstance which we fear will prove fatal to the hypothesis is, that this cloud is frequently seen in the night, a fact which we do not hesitate to adduce, notwithstanding the positive assertion of our author to the contrary. Every one who has viewed the sublime spectacle of a moonlight evening, must have observed how much the beauty of the scene has been occasionally heightened by the large round masses of cloud, which not unfrequently sail across the firmament, and "turn forth their silver linings on the night."

The length to which we have protracted this article, will oblige us to pass over very briefly the remaining parts of the essay. The cirrus is conceived to be a cloud acting the part of a conductor of the electric fluid, between different regions of the atmosphere which were in different states of electricity. We have some additional remarks on the produc tion of rain. The principal circumstance which causes the discharge of clouds is an excessive influx of vapour, accompa nied with a decrease of temperature; but it appears that this combination alone is not sufficient, without the concurrence of the stratus and the cumulus. We believe that the author farther conceives, that these clouds must possess different states of electricity, though this is rather implied than directly asserted. Upon the whole, these remarks upon rain appear to us not so perspicuous as some other parts of the essay.

We have been induced to take a pretty extensive review of this short treatise, because we think it an impor tant work on an important subject. Mr. Howard has entered on an interesting field of investigation, and he has marked out a path which must terminate in something valuable. At present, however, we regard his exertions rather as well directed, than as completely successful. Though we have taken the liberty to criticize his present perform ance, we expect more from his future