These investigations were followed by a very interesting series of experiments on the conducting power of fluids for heat, and, although he pushed his conclusions further than his experiments warranted, he showed conclusively that convection currents are the principal means by which heat is transferred through the substance of fluids, and described how, when a vessel of water is heated, there is generally an ascending current in the centre, and a descending current all round the periphery. Hence it is only when a liquid expands by increase of temperature that a large mass can be readily heated from below. Water below 39° Fahr. contracts when heated. Rumford, in his paper, enlarges on the bearing of this fact on the economy of the universe, and the following extracts afford a good specimen of his style, and justify some of the statements made by Cuvier in his eulogy:—
I feel the danger to which a mortal exposes himself who has the temerity to undertake to explain the designs of Infinite Wisdom. The enterprise is adventurous, but it cannot surely be improper.
The wonderful simplicity of the means employed by the Creator of the world to produce the changes of the seasons, with all the innumerable advantages to the inhabitants of the earth which flow from them, cannot fail to make a very deep and lasting impression on every human being whose mind is not degraded and quite callous to every ingenuous and noble sentiment; but the further we pursue our inquiries respecting the constitution of the universe, and the more attentively we examine the effects produced by the various modifications of the active powers which we perceive, the more we shall be disposed to admire, adore, and love that great First Cause which brought all things into existence.
Though winter and summer, spring and autumn, and all the variety of the seasons are produced in a manner at the same time the most simple and the most stupendous (by the inclination of the axis of the earth to the plane of the ecliptic), yet this mechanical contrivance alone would not have been sufficient (as I shall endeavour to show) to produce that gradual change of temperature in the various climates which we find to exist, and which doubtless is indispensably necessary to the preservation of animal and vegetable life....
But in very cold countries the ground is frozen and covered with snow, and all the lakes and rivers are frozen over in the very beginning of winter. The cold then first begins to be extreme, and there appears to be no source of heat left which is sufficient to moderate it in any sensible degree.
Let us see what must have happened if things had been left to what might be called their natural course—if the condensation of water, on being deprived of its heat, had followed the law which we find obtains in other fluids, and even in water itself in some cases, namely, when it is mixed with certain bodies.
Had not Providence interfered on this occasion in a manner which may well be considered miraculous, all the fresh water within the polar circle must inevitably have been frozen to a very great depth in one winter, and every plant and tree destroyed; and it is more than probable that the region of eternal frost would have spread on every side from the poles, and, advancing towards the equator, would have extended its dreary and solitary reign over a great part of what are now the most fertile and most inhabited climates of the world!...
Let us with becoming diffidence and awe endeavour to see what the means are which have been employed by an almighty and benevolent God to protect His fair creation.
He then goes on to explain how large bodies of water are prevented from freezing at great depths on account of the expansion which takes place on cooling below 39° Fahr., and the further expansion which occurs on freezing, and mentions that in the Lake of Geneva, at a depth of a thousand feet, M. Pictet found the temperature to be 40° Fahr.
"We cannot sufficiently admire the simplicity of the contrivance by which all this heat is saved. It well deserves to be compared with that by which the seasons are produced; and I must think that every candid inquirer who will begin by divesting himself of all unreasonable prejudice will agree with me in attributing them both to the same Author....
"But I must take care not to tire my reader by pursuing these speculations too far. If I have persisted in them, if I have dwelt on them with peculiar satisfaction and complacency, it is because I think them uncommonly interesting, and also because I conceived that they might be of value in this age of refinement and scepticism.
"If, among barbarous nations, the fear of a God, and the practice of religious duties, tend to soften savage dispositions, and to prepare the mind for all those sweet enjoyments which result from peace, order, industry, and friendly intercourse; a belief in the existence of a Supreme Intelligence, who rules and governs the universe with wisdom and goodness, is not less essential to the happiness of those who, by cultivating their mental powers, HAVE LEARNED TO KNOW HOW LITTLE CAN BE KNOWN."
Rumford, in connection with his experiments on the conducting power of liquids, tried the effect of increasing the viscosity of water by the addition of starch, and of impeding its movements by the introduction of eider-down, on the rate of diffusion of heat through it. Hence he explained the inequalities of temperature which may obtain in a mass of thick soup—inequalities which had once caused him to burn his mouth—and, applying the same principles to air, he at once turned his conclusions to practical account in the matter of warm clothing.
After an attempt to determine, if possible, the weight of a definite quantity of heat—an attempt in which very great precautions were taken to exclude disturbing causes, while the balance employed was capable of indicating one-millionth part of the weight of the body weighed—Rumford, finding no sensible effect on the balance, concluded that "if the weight of gold is neither augmented nor lessened by one-millionth part, upon being heated from the point of freezing water to that of a bright red heat, I think we may very safely conclude that ALL ATTEMPTS TO DISCOVER ANY EFFECT OF HEAT UPON THE APPARENT WEIGHTS OF BODIES WILL BE FRUITLESS." The theoretical investigations of Principal Hicks, based on the vortex theory of matter and the dynamical theory of heat, have recently led him to the conclusion that the attraction of gravitation may depend to some extent on temperature.
A series of very valuable experiments on the radiating powers of different surfaces showed how that power varied with the nature of the surface, and the effect of a coating of lamp-black in increasing the radiating power of a body. In order to determine the effect of radiation in the cooling of bodies, Rumford employed the thermoscope referred to by Cuvier. The following passage is worthy of attention, as the truth it expounds in the last thirteen words appears to have been but very imperfectly recognized many years after it was written:—