DANIELL'S METEOROLOGY.
WERE this book now published for the first time, it would be a remark- able work. But, to appreciate the full extent of the author's powers, it must be kept in mind that the first edition of the Meteorological Essays appeared in 1823—nearly a quarter of a century ago. Many invaluable, carefully conducted series of observations, which might otherwise be ima- gined to have supplied materials for Mr. Daniell's theory, are in fact mere corroborations of what his genius had previously divined; not a few of them were instituted with a view to test the correctness of his combinations and inferences. The Meteorological Essays are still, in all their great features, abreast of the rapid progress of meteorological science in our day ; and, more than that, they have been among the principal means of making the science what it is.
The essay "On the Constitution of the Atmosphere" is one of the most beautiful and successful of recorded efforts to advance knowledge by the synthetic method. The discoveries of analytical science and the results of observation are built up into an hypothetical system; and this system is compared with and corrected by the actual phenomena of nature, until the coherence of all its parts and its correspondence with external exis- tences afford a guarantee of its soundness. It is only by being from time to time subjected to such a process of elaboration that the frag- mentary results of observation and experiment become real knowledge. The mere observer, who sees nothing but details—still more, the mere experimenter, who sees them only modified by subjection to his own ar- bitrary treatment—never can elevate himself to comprehend nature as a whole. Comprehensive and combining spirits, like Aristotle, Des Cartes, and (in his own field of study) Daniell, give us at least something ap- proximating to the truth as it really exists : their theories suggest new experiments, and practical applications of the results of older ones ; and the efforts of kindred spirits to criticise and modify, correct, disprove, or establish their systems, is the process by which the social intellect is car- ried on in its unremitting approach towards the knowledge of the truth. Mr. Daniell brought to his task a rare natural talent, long and exten- sively cultivated for experimental analysis. It could have been wished that his acquaintance with the processes of the modern geometrical ana- lysis had been more distinct and familiar ; for, as is apt to be the case with men who have intelligence sufficient to feel its value but not prac- tice sufficient to use it with certainty and complete command, he has sometimes rather darkened than cleared his meaning by its indiscriminate application. This drawback, however, is diminished by the compensating power of the instinct of genius : the matter of the essay on the Constitu- tion of the Atmosphere is substantially valuable ; and its great outlines are artistically beautiful, though there may be awkwardnesses in some of the details.
Mr. Daniell found an immense quantity of careful and valuable ob- servations on atmospheric phienomena ready to his use. The writings of Luke Howard alone are a mine of treasure. In addition to these ,he had at his command the results of the labours of an age distinguished, if by any one thing more than another, by the splendour of its chemical analysis and mechanical combinations. Analysis had resolved the at- mosphere into its elements, and almost exhausted experiment upon each of them separately. The various modes and pressures of mechanical forces had been no less elaborately investigated. As Mr. Daniell said at the outset of his labours-
" The elements of the science, considered as founded upon experiment and ob- servation, have been largely extended and deeply explored; and a rich accumula- tion of facts has been collected, which only require perhaps to be properly adjusted to enable us to raise the superstructure with security. I reflected, that in the present state of our knowledge, this might be donesynthetically with thegreatest advantage; and that by setting out from a few plain and established principles, and by accurately appreciating their mutual influences, there was a probability of ascending with security to more complicated relations; till at length, by gradual structure, we might possibly accomplish the explanation of those atmospheric phrenomena, the analysis of which has hitherto been perplexed with insurmount- able difficulties."
To this end, he proceeded from the assumption that the air is a homo- geneous fluid, the constituent elements of which are known, through which is disseminated a large amount of aqueous vapour ; the whole mass, inert in itself, like all matter, being acted upon by the antagonist powers of gravity and heat,. His own words better than any others will ex- plain the method of his going to work upon this assumption. " It appears to me, that the deductive method may be most advantageously applied to the gradual development of the complex phmnomena of the atmospheric
ocean. * • In adopting this method, I divide the inquiry into four sections. In the first, I consider the habitudes of an atmosphere of perfectly-dry, perma- nently-elastic fluid, under certain conditions; in the second, those of an atmo- sphere of pure aqueous vapour; in the third, the compound relations of a mixture of the two; and in the fourth, I endeavour to apply such principles as may legitimately be deduced from the previous investigation, to some of the observed phrenomena of the atmosphere of the earth."
Common sense, without any minute acquaintance with scientific in- quiry, will at once enable any one to see the probability that such a mode of investigation would yield valuable results. A few years after the publication of the first edition of the Essays, Captain Basil Hall commu- nicated to the author a valuable paper on the Trade Winds, the result of extensive personal observation ; which showed that Professor Daniell, by reflection in his closet, had formed a more correct notion of that phieno- menon than many who had enjoyed opportunities of observing it, yet continued unthinkingly to repeat the inaccurate accounts of others. The valuable and extensive accumulations of observations made during the Arctic and other expeditions of discovery instituted by the British Govern- ment, contributed many equally striking corroborations of Mr. Daniell's inferences. Nor was he himself idle. He devised new experimental in- struments, (his dew-point hygrometer has done almost as much to give a new form to meteorology as his essay,) and instituted delicate and in- genious experiments, for the purpose of correcting and extending his views. The discoveries of Melloni respecting the different powers of the rays of heat, and the effect of radiation upon them—the discoveries of Faraday in electricity—everything, in short, adapted to modify and recti- fy his opinions—was caught at and brought to bear upon his system. His essays on the oscillations of his barometer, on the radiation and ab- sorption of heat in the atmosphere, and on various meteorological instru- ments, are interesting evidence of his unmeasured conscientious activity.
For the general reader, not the least pleasing and important of Mr. Daniell's works are his practical writings. The essays on the Climate of London, and " on Climate considered with regard to Horticulture," gave a new impulse to that most delightful and peculiarly English art.
The essays of Mr. Daniell form an epoch in the history of meteorolo. gtcol science. His writings are not merely a monument of the state of the science as it existed in his time—as he himself had made it—they have been a momentum to that farther advance which is now in progress. His brief and cautious essay "on some of the Pluenomena of Atmo- spheric Electricity " may be regarded as the starting-point of those ex- tensively combined observations on electric and magnetic phrenomena, which by the assistance of most of the Governments of the civilized world are now going on simultaneously in both hemispheres. It may be added, that his Introduction to the Study of Chemical Philoscphy- a book merely intended to present to students of chemistry an elementary view of Faraday's—has been the means of training both in England and America a numerous race of competent experimenters and observers in this department. For the other labours and deserts of Mr. Daniell we must refer to his writings, and to the (somewhat meagre) biographical memoir prefixed to the Elements of Meteorology. His efforts in this science are those which will perpetuate his name. His work is accomplished—he survives no more to alter, amend, or complete. The structure must remain as it is. The critic may therefore dispense with the ungracious task of expa- tiating on minor defects—only useful when the object is to spur the author to remove them—and dwell on the more pleasant contemplation of the beauty and merit of the whole.
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