to the intimacy of Watt. In short, his shop—yes, shop! became a sort of academy, whither all the learned of Glasgow resorted to discuss points of the greatest nicety in art, science, and literature. Indeed, I could not venture to tell you what a distinguished part was taken by the young artificer of twenty-one in those learned meetings, were it not that I am borne out by an unpublished notice of the most illustrious contributor to the Encyclopædia Britannica. "When I was as yet a young student," says Robison, "I had the vanity to think myself a pretty good proficient in my favourite studies of mathematical and mechanical philosophy, and, on being introduced to Watt, was rather mortified at finding him so much my superior. * * Whenever any puzzle came in the way of any of us, we went to Mr. Watt. He needed only to be prompted; every thing became to him the beginning of a new and serious study, and we knew that he would not quit it till he had either discovered its insignificancy, or had made something of it. *** On one occasion, the solution of a problem seemed to require the perusal of Leupold's Theatrum Machinarum; and Watt forthwith learnt German. At another time, and for a similar reason, he made himself master of Italian. *** When to the superiority of knowledge, which every man confessed, in his own line, is added the naïve simplicity and candour of Mr. Watt's character, it is no wonder that the attachment of his acquaintances was strong. I have seen something of the world, and am obliged to say, that

I never saw such another instance of general and cordial attachment to a person, whom all acknowledged to be their superior. But this superiority was concealed under the most amiable candour, and liberal allowance of merit to every man. Mr. Watt was the first to ascribe to the ingenuity of a friend things which were very often nothing but his own surmises followed out, and embodied by another. I am well entitled to say this, and have often experienced it in my own case."

It is for you to determine whether the honour of having uttered these last words is not as great as that of having inspired them.

The studies thus deep and various, into which the singular circumstances of his position incessantly threw the young Glasgow artist, never interfered with the labours of the work-shop. These he executed by day; the night was devoted to theoretical researches. Trusting to the resources of his imagination, Watt seemed to find pleasure in the most difficult undertakings, and those for which he might have been deemed the least fitted. He was altogether insensible to the charm of music, and never learned to distinguish one note from another, -the ut, for instance, from the fa,-and will it be believed that he undertook to build an organ ? Yet the work was brought to a good end; it is needless to say, that the new instrument displayed the most important improvements in its mechanical parts, in the stops, in the indicators and regulators of the strength of the blast; but you will be astonished to learn, that its harmonic qualities were not

less remarkable, and delighted the best performers. Watt solved an important part of the problem; he found out the temperament assigned by a master of the art, by help of the phenomena of the beats of imperfect consonances, then very ill understood, and of which he could have gained no knowledge except from the profound, but very obscure work of Dr. Robert Smith of Cambridge.*

HISTORY OF THE STEAM-ENGINE.

I HAVE now come to the most brilliant period of Watt's life, and also, I am afraid, to the most difficult part of my undertaking. undertaking. As to the immense importance of the inventions which are now to be the subject of my discourse, no doubt can possibly be entertained; but I fear that I cannot make them be appreciated as they deserve, without going into very minute numerical comparisons. In order that these comparisons, if indispensable, may be readily understood, I shall now lay before you, as briefly as possible, the nice doctrines of Natural Philosophy on which we shall have to rest them.

* See the article TEMPERAMENT in the Encyclopædia Britannica, which is given in Brewster's edition of Robison's Mechanical Philosophy, vol. iv. p. 412. The title of Dr. Smith's book is, "Harmonics, or the Philosophy of Musical Sounds, by Robert Smith, D.D., F.R.S., and Master of Trinity College, in the University of Cambridge." The first edition of this work was published at Cambridge in 1749; the second, much improved and augmented, at London in 1759.-TR.

By the effect of a mere change of temperature, water may exist in any one of three states, quite distinct from each other. These are the solid, the liquid, and the gaseous or vapour state. Below zero in the scale of the centigrade thermometer, [32° of Fahrenheit] water becomes ice; at 100°, [212° Fahrenheit] it turns rapidly into vapour; at all the intermediate degrees it is liquid.

A close observation of the points of transition from one of these states to another, leads to discoveries of the utmost importance, which form the key to the economical appreciation of steam-engines.

Water is not necessarily warmer than all kinds of ice; water may remain at a temperature of zero [centigr.] without freezing; ice may remain at zero without melting; but there is great difficulty in believing that this water and this ice, both at the same degree of temperature, both at zero, differ only in their physical qualities; or that no element, other than water, properly so called, distinguishes the solid from the liquid water. A very simple experiment will throw light on this mystery. Mix a kilogram* of water at zero, with a kilogram of water at 75°, centigrade. The two kilograms of mixture will have a temperature of 37 degrees; that is to say, the mean temperature of the two component liquids. The hot water is thus found to have retained 37° of its former tem

* A kilogram is 2-679514 lbs. troy, or 2:204857 lbs. avoirdupois.-TR.

perature;—it has communicated the other 37° to the cold water. All this is quite natural, and might have been anticipated.*

Let us, however, repeat the experiment with one single difference. In place of the kilogram of water at zero, let us take a kilogram of ice at the same temperature of zero. From the mixture of this kilogram of ice with the kilogram of water at 75°, will result two kilograms of liquid water, because the ice, steeped in hot water, will certainly be dissolved, and will continue of the same weight as before. But were you to attribute to the mixture, as in the former instance, a temperature of 37°, you would be deceived; the temperature here will only be zero,—there will remain no trace of the 75° of heat which the kilogram of water possessed; these 75° will have separated the atoms of ice from each other, and will have blended with them, but without heating them in any way whatsoever.†

I have no hesitation in offering this experiment of Black as one of the most remarkable in modern

* "When hot and cold water are mixed together, the excess of heat contained in the hot water is equally distributed in an instant through the whole mixture, and raises the temperature of it according to the greatness of the excess of temperature, and the proportion which the hot water bore to the cold. If the quantities of hot and cold water are equal, the temperature is the middle degree between that of the hot and that of the cold." See Dr. Black's Lectures on Chemistry, vol. i. p. 122. Edit. 1803.—Tr.

+ The fact is stated by Dr. Black in these words :—“ I have, in the same manner, put a lump of ice into an equal quantity of water, heated to the temperature of 176°, and the result was that the fluid was no hotter than water just ready to freeze." Black, vol. i. p.

125.-TR.

B