will disprove the consistency of his supposition with the opinion of such emanations; and the other proves the consistency of his two suppositions, and, at the same time, confers a high probability on the real existence of these emanations. The experiments are exceedingly obvious, and I take to myself no merit for having suggested them. I only mention them as a specimen of that spirit of monopoly and exclusion which extends to more of the Edinburgh professors than to Dr. Hope. He told me that he had not read all my paper when I called upon him, nor had performed any of the experiments which I proposed. He evidently did not understand them. His objections were so trifling and absurd, that I am ashamed to think they came from the mouth of a professor. He obliged me to repeat my meaning half a dozen of times, and seemed to be laboring under the desire of saving himself the indignity of being dictated to. I at last, however, extorted from him a faint and reluctant acknowledgment of the validity of my reasonings; but he wished to arrogate to himself the anticipation of what I suggested. I told him that I thought that we were warranted to speak of Dr. Hutton's opinion in a more decided manner than he had done in the class; and, upon the whole, can not blame myself with having expressed myself throughout in a forward or disrespectful manner. Though the experiments are obvious, yet I suspect they have not yet occurred to the consideration of chemists. As the radiation of cold is a new subject, Dr. Hope having exhibited the phenomenon to Count Rumford last summer for the first time, it is upon this phenomenon that Count Rumford now rests the principal weight of his arguments for heat consisting in the vibrations of the minute particles of bodies. "I have come on pretty well in the way of pupils. I have got a mathematical one from Mr. Playfair, and have two other pupils beside. I attend Mr. Stewart's first class. I have only seen him twice since I came to Edinburgh, and that for a very short time. I am yours, with esteem, THOMAS CHALMERS. "DR. JAMES BROWN." "I apprehend that Dr. Hutton's opinion respecting the radiation of cold admits of being either refuted or confirmed by the following simple experiment: "If, as he says, the reduction of temperature in the bulb of the thermometer arises not from any positive efficiency exerted by the cold, but merely from less heat being radiated by the cold body than by an equal portion of atmospherical air, it is evident that if a vacuum be formed in the focus of the concave mirror, no rays at all will be emitted, and consequently a still greater reduction of temperature will ake place. "If the thermometer is placed indifferently without the reach of any of the mirrors, it will exhibit the temperature of the room; place it in the focus of a concave mirror A, the consequence is, a small elevation of temperature; for though the rays from any object in the axis of the mirror do not light upon the mirror in a parallel direction, yet, as you remove from the mirror, the divergency of these rays is so small, that though not accurately collected in a point, they fall in great abundance upon the bulb, and raise its temperature. It is impossible to say, à priori, whether, if you now place another concave mirror B in the axis of this mirror, it will have any effect in producing a further elevation of temperature. Certain it is, that the air in the focus of the mirror B is more powerful than before, because its emanating rays are more accurately collected in the bulb of the thermometer; but, again, the divergent rays from the more remote portions of air are thereby intercepted. However this be, it does not affect the validity of the second method, which I humbly propose for determining the truth of Dr. Hutton's opinion. Let both the mirrors still retain the same place; let the cold body be placed in the focus A, and let the temperature upon the bulb in B be observed. The deviation of this temperature from the temperature of the room arises from the joint effect of those rays which are accurately collected from the cold body, and those rays which are less accurately collected from the intermediate axis between the mirrors. Let the mirror A, in whose focus the cold body is placed, be now turned round, and observe the change of temperature which ensues when the convex side of it is now presented to the cold body. The change, whatever that be, is owing solely to the collected emanations of the cold body being now removed from the bulb of the thermometer, for all other circumstances remain the same. The divergent rays from the more remote parts of the axis are still intercepted by the mirror A, and those in the intermediate part of the axis fall on the mirror B as before, and have the same effect on the temperature of the bulb. Hence, if this change be an increase of temperature, it proves that the emanation from the cold body had a positive efficiency in reducing the temperature, since the abstraction of these emanations increases that temperature. But if the change be a reduction of temperature, it proves that the abstraction of these emanations is a diminution of caloric, and that the arguments which those who oppose the materiality of heat derive from this phenomenon fall to the ground. I hope that my total unacquaintance with the present state of chemical knowledge will excuse any thing which appears trite or familiar in these observations. "THOMAS CHALMERS." "EDINBURGH, Feb. 25, 1801. "DEAR SIR-1 received your very kind letter some weeks ago, and am much obliged to you for your instructive observations. I met with Dr. Hope some time after, who told me that he had looked over my paper with more attention, and found it was correct. I am not sure what to understand by this-if he admits the justness of its hypothetical reasonings, or if he has performed the experiment, and obtained any new or original result. He went off without telling me any more particulars, and though I have met with him several times since, he has never mentioned any thing more of the subject. I am yours, with sincerest esteem, THOMAS CHALMERS. "DR. JAMES BROWN." The letter which follows was addressed to James Wood, M.D., now of Edinburgh, who had interested himself in obtaining the offer of a situation for Mr. Chalmers: "EDINBURGH, April 3, 1801. "DEAR SIR-I received yours about an hour ago, and am extremely obliged to you for the friendly concern you have manifested in my behalf. I have determined not to go; but the interest you have taken in my welfare demands a more particular explanation. The office itself is highly agreeable to my wishes, and is as much superior to my professional prospects, as the manly energy of active life is to be preferred to the habits of mawkish indolence and retirement, so incidental to the situation of a clergyman. But there are reasons, which you have in part anticipated, that oblige me at present to an opposite determination. In the first place, I would not, without the greatest reluctance, interrupt the course of my present studies, which for the last winter have been chiefly directed to that most interesting of subjectschemistry. In the next place, I have some engagements in the way of teaching, which, though they may be got over, yet can not well be relinquished without a degree of indelicacy. In the third place, and chiefly, I cherish some faint, yet I hope well-founded prospects of preferment in this country in a line I prefer above all others—the teaching of mathematics. This is not generally known among my friends, and their ignorance of it may perhaps incline them to charge my determination with folly. In the last place, independently of such preferment, I think the interval between leaving the college and entering into the office of a clergyman can not be more profitably employed than in extending my acquaintance with science. These reasons, added to the uncertainty of entering into the situation, will, I hope, justify me in your opinion for not availing myself at present of your obliging recommendation. I feel a sentiment of gratitude for your kindness which I do not express. I may be deficient in the language of acknowledgment, but I confide in the liberal interpretation of a candid and enlightened mind. "I attend the two classes you mention. I was a little disgusted at first by that foppery of manner and language which distinguishes the lectures of Dr. Hope; but the mind soon accommodates to the influence of custom; and I must say, upon the whole, he is a good professor. He explains the different actions with a simplicity and familiarity which I did not expect. He does very well as long as he confines himself to the particular doctrines of chemistry, but is miserably poor, I think, in his general discussions upon the nature and objects of the science. "Have you observed that Mr. Stewart uniformly avoids every subject which involves any long or difficult discussion? And yet occasional appearances of ingenuity and penetration, and even of a systematic comprehensive tone, render it difficult to say whether this is to be altogether ascribed to want of ability. I disagree with him in the leading features of his philosophy, particularly on the subjects of liberty, physical and efficient causes, and the indications of design in the uni verse. "There is nothing occurring at present particularly interesting. Dr. Gregory, you will know, has gained his cause, to the great mortification of the surgeons in town. The chemistry class was never so full as it is this winter. I know that Dr. Hope has not below 350 students. This is wonderful, considering the abilities of his rivals, Drs. John and Thomas Thompson. The latter is giving particular satisfaction his plan is altogether original. It is quite the synthetic mode of communication. He arranges bodies according to the simplicity of their composition-begins with the elementary substances, and proceeds to the more complicated. This plan is perhaps the more philosophical, and to be preferred, on account of its simplicity, and the aid which it affords the memory. At the same time, I have felt advantages in prosecuting a subject according to the natural or theoretical order of discovery. You will recollect, in particular, Dr. Robison's method of discussing astronomy. "With best wishes for your welfare, I am, dear sir, your most obedient humble servant, THOMAS CHALMERS." "During one session at Edinburgh he attended the lectures of the celebrated Mr. Stewart. One day, while conversing with him respecting that distinguished individual, he asked me what I thought of his lectures? To this I replied, that I thought them very elegant, and that I believed they were very useful; but that I frequently lost him, or, in other words, was not able at times to follow him in the train of his discussions. He immediately said, 'I never lost him'―at which I was greatly surprised; 'but,' he added, 'that owing to his numerous and long digressions, and to the variety of quotations which he read from those authors which had a reference to his subject, he never knew where he was.'"-MS. Memoranda of Dr. Chalmers, by the Rev. Mr. Smith. APPENDIX, D.-P. 87. EXTRACT FROM INTRODUCTORY LECTURE TO A COURSE OF CHEMISTRY. Chemistry is one of the most interesting and dignified of pursuits. It has all the charm and freshness of novelty to recommend it. It is fast hastening to perfection. It is daily extending its triumphs. The annals of every year are recording some new and important discovery, and its cause is supported by the labors of more than half the philosophers of Europe. A mind devoted to the interests of science, you can easily conceive, will sigh for an opportunity of teaching it. Such a mind rejoices in communication; it rejoices in imparting to all around that enthusiasm which animates its own exertions; it rejoices in awakening among its hearers the flame of emulation and enterprise, and triumphs in the silence of their attention as the most flattering of all testimony. Let it not be disguised—I look on these hours which are consecrated to the labors of instruction as the most important and delightful exercise of my powers, and exult in the office of an instructor as the proudest station which a man can occupy... "When introducing a new science, it is customary to begin at the first period of its discovery, to unfold the progress of its improvement, to pursue the successive steps of its history, and to settle its metaphysics and first principles on an unquestionable foundation. This order I reprobate as unnatural. It is altogether unfit for the purposes of instruction. The history of a science can never be delivered without a perpetual recurrence to that phraseology which is peculiar to it -a phraseology which, at the commencement of your studies, you are not prepared to understand. There is nothing that I am more cordially disposed to execrate than an ostentatious parade of technicals; a pitiful attempt to excite the stare and astonishment of ignorance; the wretched ambition of exhibiting yourself to a gaping populace as a great philosopher, a wonderful head-piece, a stupendous intellect, read in the mysteries of nature, and versed in all the lore of antiquity. My sole object in instituting a course of lectures upon chemistry is to introduce you to one of the most useful departments of philosophical investigation. I wish to divest it of that mysterious attire in which it has too often repelled the attempts of the solitary and unassisted inquirer. It may be remarked of chemistry, with more justice than of any other science, that it is seldom a self-taught acquirement. taste for chemistry is seldom derived from the mere perusal of chemical treatises, or from the efforts of solitary reflection. To be a chemist, you must have frequented the instructions of some chemical teacheryou must have repaired to some hall of chemical experiments-you must have familiarized your conceptions to the subjects of chemistry by the actual exhibition of these subjects to the senses. You are miserably mistaken if you think you can derive the same from the A |