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(No thanks to wind, or sail, or working rill)
Compared with thee,
* Thou best Philosopher made out of wood !
A “ Walking Stewart !”—pp. 72–74. In this production the great patron of Moxon may be said to have outdone himself. Pindar, were he to revisit this earth and read these lines, would lament that the tread-mill had not been invented in his time. What a noble theme would its rotatory motion and its sorrow-compelling-power have furnished to his muse! Oh that there were a tread-mill for the poetasters of our day! Thee, Charles Lamb, thee, Robert Montgomery, thee, Professor Wilson, thee, Shepherd of Ettrick, and ye, ye crowd of culprits who have brought down Blackwood and the New Monthly to one dead level of poetic dullness, and cumbered the stalls with your absurdities, then we should with gladness behold treading the endless circle ! Fit emblem of your own muses, ever straining, never rising, labouring hard, little producing, expiating
your sins without mending your rhymes, and consuming a thousandfold more than you earn How far such a publisher as Mr. Moxon ought to be considered as an accomplice in your transgressions, is a question that could admit of no doubt. He ought to be adjudged the greatest offender of all, and the least degree of punishment assignable to such a convict, should be to give him an hour or two in the hopper.
Art. VI.--An Outline of the Science of Heat and Electricity.—By
Thomas Thornson, M.D., Regius professor of the University of Glasgow. 8vo. pp. 583. London: Baldwin and Cradock; and Edinburgh:
William Blackwood. 1830. This admirable work supplies a great desideratum to the student in chemistry and natural philosophy, namely, a complete view of the phenomena of Heat and Electricity, as those phenomena have been detected and explained up to the present time. We may very well say that a thorough acquaintance with the laws of these two great principles is the foundation of all chemical knowledge, inasmuch as they are the chief agents in effecting those multitudinous changes of substances, which it is the business of chemistry to mark and expound. The high and deserved reputation of Dr. Thomson induced us to expect a volume which would, in every respect, answer the description of a standard performance for the service of the present generation. We have not been disappointed. The comprehensive acquaintance of the learned professor with every branch of his subject, is scarcely less to be admired than the lucid and elegant simplicity in which his vast information is conveyed. A child will understand his text-a philosopher will delight in it. Until
our own times, very incorrect notions were entertained respecting the nature of Heat. A vast deal has been done by scientific persons in Great Britain, to collect just information on this great subject, and the name of Bacon must ever be identified with it as among its most useful illustrators. It is impossible yet to say what Heat really is; and the best of our philosophers have not been able to ascertain whether or not Heat be an original and independent principle, or merely an attribute dependent on the existence of the matter with which it is found allied. Dr. Thomson, we hope, goes too far when he says that all the knowledge which we possess, or can ever acquire, respecting Heat, is that of the different effects which it produces upon bodies.' Who, fifty years ago, would have supposed that a generation such as the present one, was so near at hand, which would take the liberty of superseding the winds of heaven--those venerable and worshipped controulers of navigation,--and would choose to be steered right and left, for pleasure or commerce, by the vapour of a tea-kettle? Many have been the futile attempts to place limits to the progress
of discovery; nor should we be in the least surprised that Dr. Thomson, one day or another, by finding out the exact principle of Heat, should raise a laugh in the scientific world, against the temerity of his own predictions. One of the principal effects of Heat is that of expanding bodies, whether solid, liquid, or in a gaseous state.
With this branch of the subject of heat, is connected, of course, the thermometer, of the history of which we have an excellent account by Dr. Thomson.
The invention of the thermometer, like that of gunpowder, is involved in considerable obscurity. Drebbel, a physician at Alkmaer in Holland, is stated by Boerhaave to have made thermometers about the beginning of the 17th century. Sanctorio, the celebrated founder of statical medicine, who was a professor at Padua at the commencent of the 17th century, lays claim to the invention of the thermometer. And this claim is sanctioned by Borelli, who gives us an engraving, together with a description of the original thermometer of Sanctorio. Malpighi, also, who was a professor at Pisa, and the intimate friend of Borelli, ascribes in his posthumous works the original invention of the thermometer to Sanctorio. These testimonies are sufficient to satisfy us that Sanctorio was the first person who thought of constructing a thermometer, at least in Italy, which was at that period the peculiar seat of the sciences.
Sanctorio's thermometer was merely a glass tube with a ball blown at the extremity, the open end of which, after the air had been somewhat rarefied, was plunged into a coloured liquid. When the air cooled it resumed its original bulk nearly, and a portion of the coloured liquid rose in the tube. This tube was divided into a number of equal portions, called degrees. When the temperature of this tube was raised, the air in it expanded, and the coloured liquid sank in the tube. When its temperature was lowered, the bulk of the air diminished, and the coloured liquid rose in the tube. The number of degrees which the coloured liquid rose or fell indicated the change of temperature. Thus Sanctorio's instrument was what is called an air thermometer; the changes of temperature being indicated by the alterations in the volume of the air confined in the tube. As the tube was plunged into an open dish filled with coloured liquid, it is evident that the rise and fall of that liquid would be affected not merely by alterations in the temperature, but also by all changes in the density of the atmosphere. When the barometer stood high, the liquid would be more elevated in the tube than when the barometer was low, even supposing no alterations in the temperature.
"The Florentine academicians about the middle of the 17th century made the first improvement on thermometers. They employed a long glass tube, blown at one extremity into a ball, which they filled up to a certain mark in the tube with spirit of wine. The extremity of the tube was then sealed hermetically, by melting it by a blowpipe. The tube was afterwards divided into 100 equal parts, called degrees, by means of small particles of white enamel. Boyle claims for himself the merit of first introducing such sealed instruments into England. At first, he says, no one would believe that a liquid would expand and contract in a tube hermetically sealed. But he convinced himself of the fact by actual trial, and was still farther
satisfied by the sight of a small thermometer constructed in this
* About the beginning of the 18th century, Mr. Fahrenheit, originally a merchant in Dantzic, who, after failing in business, settled at Amsterdam as a thermometer maker, substituted mercury for spirit of wine, and greatly diminished the size of the tube and the bulb. This rendered the instrument capable of measuring much higher degrees of temperature ; for mercury does not boil till raised to a much higher temperature than spirit of wine.
· The instrument, as originally made, laboured under a great defect, and many years elapsed before philosophers thought of the proper remedy. No two instruments agreed with each other. The scale of degrees applied to the tube was quite arbitrary. It was differently constructed and differently applied in every thermometer; and experiments made with one could not be usnally compared with those made with another.
· The most important improvement in these instruments was the contrivance of a method of applying their scales so as to make them agree with each other when exposed to the same temperature, whatever that may be. This was attempted by different methods in different parts of Europe, till at last one was hit upon so superior to all the rest, that it was soon universally employed.
• Sir Isaac Newton seems to have first proposed this method ; and Fahrenheit was probably the first thermometer maker that put it into practice. It is founded on two discoveries made by Dr. Hooke. The first in 1664, the second in 1684. It was observed by Dr. Hooke that water is changed into ice when cooled down to a particular temperature, and that this temperature remains the same all the time that the water is changing into ice, or the ice into water. If we take a thermometer and plunge it into melting snow, taking care that the ball be completely covered, the quicksilver will be contracted by the cold and descend in the tube.
It will at last stop and continue at the same place so long as any considerable part of the snow remains unmelted. If we now mark the part of the tube at which the mercury stopped, and repeat the experiment with the same thermometer however often, and at places and times however distant, the result will always be the same, the mercury will always descend to the same part of the tube to which it descended the first time, and will remain stationary there so long as any considerable part of the snow remains unmelted. This shows that melting snow is always equally cold, or has the power of reducing the thermometer to one steady density, which may be called the melting snow expansion of the quicksilver.
The second discovery of Dr. Hooke was of a similar nature. He found that other things being the same, water always begins to boil at the same temperature. If, therefore, we take the thermometer used in the preceding experiinents, immerse it in boiling water, or surround it with steam, and keep the liquor boiling around it for some time, the mercury will ascend to a certain point in the tube, and however long we continue to boil the water, it will ascend no higher. If we mark the part of the tube to which the mercury rose, and afterwards repeat the experiment ever so often in places of the same height above the surface of the sea, and when the height of the barometer is the same, the mercury will always rise to the same point as the first time. Thus boiling water has the power of bringing
mercury to another determinate state of expansion, which may be called the boiling water expansion of mercury.'-pp. 36—41.
The following practical observations deserve the attention of every man who uses a thermometer :
The thermometer merely indicates the change of temperature which it undergoes itself, when applied to a hot or cold body. It will not give us a direct idea of the temperature of another body into which we plunge it, unless it bears a very small ratio in point of size to that of the body under examination. We must wait for some time till the thermometer become stationary before we draw our conclusion. If the temperature of the body examined be undergoing alteration, (either augmenting or diminishing,) the size of the thermometer applied ought to be very small, that it may acquire the temperature of the body to which it is applied as rapidly as possible. Indeed, if the thermometer be of a considerable size, it will never indicate the maximum temperature of a body, provided that temperature be of short duration. I suspended a very large and a very small thermometer near each other in a north exposure, and shaded from the sun, to determine the summer temperature of Glasgow; and I almost constantly found the small thermometer a degree or two higher than the large one, about the time of the day when the temperature was highest, and a degree or two lower when the temperature was coldest. The mean temperature of the day indicated by each thermometer corresponded, but the extremes differed several degrees.
• The temperatures which we can measure by a mercurial thermometer are confined within narrow limits. For mercury freezes at about 39° below zero, and boils at 660°. Hence we cannot employ it to measure greater heats than 660°, nor greater degrees of cold than 39o. Yet many temperatures connected with our most common processes are much higher than 660°. The heat of a common fire, the temperature at which silver, copper, and gold melts, and many other such points, offer familiar examples.'pp. 49–50.
The radiation of heat is admirably explained in this volume. We need scarcely say that this property is no more than the power which heat has of passing off from the surfaces of bodies in straight lines. The subject is one which interests us all, since it explains many of the natural phenomena by which our curiosity is arrested, or from which, in our imperfect state on this earth, we derive a great deal of benefit. The phenomena of dew is referable to this property of heat, and the manner of its formation is too well stated by Dr. Thomson to allow us to pass it by.
* To understand the way in which dew is formed it is necessary to know that water is capable of being converted into vapour at all temperatures from 32 to 2120. Hence the atmosphere is seldom or never destitute of aqueous vapour. But the absolute quantity that can exist depends upon the temperature. At 32° it can contain only by th of its volume of vapour, while at 52° it can contain Goth of its volume. When air containing vapour diminishes in its temperature, a portion of its vapour is usually condensed into water. The amount of the dininution of temperature necessary to cause air to deposit moisture depends upon the quantity of