A paper of Dr Hutton " On the Theory of Rain," was published in the first volume of the Edinburgh Transac tions. It forms the only scientific explanation of the phe nomena that we have. The discovery of it evinced pro found genius and accurate information, and it will probably always be retained by meteorologists. Two portions of air of different temperatures, both saturated with humidi ty when mixed, and thus reduced to a medium tempera ture, have not the power of retaining the same quantity in a state of vapour. The reason of this is, that the quantities of humidity retained in this state proceed in a geometrical ratio, while those of temperature increase arithmetically. A larger quantity of water is retained by that heat which had kept the one portion of air above the resulting me dium, than when the same heat is employed in raising to that medium the temperature of the coldest portion. The consequence of this is, that a part of the water is precipi tated. This theory was opposed by i\lonsietu• de Luc, who maintained, that the heat was communicated from one part of the atmosphere to another without the actual intermix ture of different portions of air. Dr Hutton made several other acute improvements in meteorology, which were afterwards published in his " Physical Dissertations," in which his theory of rain was again given. It was by the theory of the earth, however, that the greatest portion of his interest was absorbed. The journeys which he made to Glen Tilt, to Galloway, the isle of Arian and St Abb's Head, supplied him with facts which afforded him exqui site delight, especially those which elucidated his peculiar views of the nature of granite, and the circumstances under which it assumed its present situation in relation to the other rocks. He supposed it to have been forced up in a state of igneous fusion by the expansive power of the cen tral heat, and injected in that state into the rents lnodnc ed in the superincumbent strata, which had previously formed the exterior crust of the-globe. It was the cout nuation of the granite upward into these rents or• veins that so much delighted Dr Hutton. This is a fact which still furnishes one of the strong points of the' Huttonian theory.
This philosopher also turned his attention to another subject suggested by his chemical pursuits, viz, the gene ral nature of matter. His doctrines on this subject are given in his" Dissertations on different subjects in Natural Philosophy." Thcy bore some resemblance to those of 13oscovielr, though somewhat different, and seem to have been with Dr Hutton altogether original. After this he published a more voluminous work, entitled a An Investi gation of the Principles of Knowledge and the Progress of Reason from Sense to Science and Philosophy," in three 4to volumes. His leading idea was, that matter is an as semblage of powers; that our ideas of external substan ces have no resemblance to the causes which produce them; and consequently that the world, as conceived by us, is entirely the creation of the mind itself, acted on by unknown external causes.
In 1793, Dr Hutton was seized with a severe and dan gerous illness from a retention of urine. When he reco vered from its severest symptoms, he continued his litera ry occupations. It was then that he prepared the work last tnentionetl 1'or publication. He was also now called on to defend his doctrine on the theory of the earth, from the arguments of i'lr Kirwan, published in the Transac tions of the Irish Academy, especially as these were ac companied by some misrepresentations which it was in cumbent on him to expose, and some charges of an odious tendency which it was necessary to repel. It was only now
that he began to publish his treaty of the earth in a sepa rate state, as it had hitherto been but partially unfolded in a variety of papers. He published two octavo volumes in 1795, and a third was left behind in manuscript.
After this he published his " Elements of Agriculture," and eminently contributed by this publication, as he had done by his former example, to give an impulse to the pro gress of that important art.
After this he suffered under a renewed and very severe attack of his complaint; and iu 1796 and 1797, his strength was greatly reduced, and his constitution broken. Still, how ever, he employed himself in reading and writing. Saus sure's Travels among the Alps, which at this time were newly pubUshed, furnished him with high entertainment, con genial with the favourite scientific amusements of his life. On Saturday the 26th ofNarch 1797 he suffered much pain, but continued to make some efiurts in study. In the even ing of that day, his complaint increased in a most rapid manner, and carried him ofF belore time was allowed for his medical attenclant to arrive.
He was undoubtedly a man powerfully qualified to ad vance science. It is yecIcotietl by some a reflec tion on the memory of any philosopher, to have been the au thor of a theory of the earth. But we have already observ ed, that such persons are not aware of the engaging nature of such speculations to a philosophical and attentive mind, to which it is a natural object of ambition, to throw a consistent light on the stupendous and mysterious appearances exhibit ccl in the mineral kingdom. Some who have studied this subject profoundly, and have embraced conclusions very dif ferent from those of Hutton, have betrayed too great prone ness to throw reflections on the degree of sottndness at tached to this author's beneral philosophical discernment. They show themselves little sensible of the uncertain na ture of all such speculations, and thus furnish greater evi dence of their own deficiencies than of those of their oppo nents. The theory of the earth should be acknowledged to be as yet an enigmatic department of science ; and the vari ous attempts which have been made to solve its dilFleuities, both those of old and those of recent date should be allowed their respective share ofplausibility, while the defects ofeach should be equally kept in view. It is a mistaken idea to sup pose, that enthusiasm in favour of one system is in any de gree necessary to keep up the spirit of science. Such an en thusiasm partakes of intemperance ;' the activity to which it gives birth is of a spurious complection, and is not of that kind which promises greatest durability. Dr. Hutton's private character was highly amiable. His manners were simple, but his conversation was animated. A combina tion of sincerity and ardour gave a charm to his company in the eyes of all his learned friends, though he was not formed on such a model as to fit him for gay or general society, which he did not relish or in any degree cultivate. His expressions in ex plainingWs views of points of science were remakably clear and forcible, and would not have led his friends to expect so much obscurity as is found in some of his writings. For an interesting view of his character and pursuits, we refer to the account of him published in the 5th volume of the Transactions of the Royal Society of Edinburgh, from the pen of his friend Professor Playfair. From that source the present short abstract has been chief ly taken. (H. D.)