To Charles Thomson
Paris Dec. 17. 1786
A dislocation of my right wrist has for three months past disabled me from writing except with my left hand, which was too slow and awkward to be employed but in cases of necessity. I begin to have so much use of my wrist as to be able to write, but it is slowly and in pain. I take the first moment I can however to acknowlege the receipt of your letters of Apr. 6. July 8. and 30. In one of these you say you have not been able to learn whether, in the new mills in London, steam is the immediate mover of the machinery, or raises water to move it? It is the immediate mover. The power of this agent, tho’ long known, is but now beginning to be applied to the various purposes of which it is susceptible. You observe that Whitehurst supposes it to have been the agent which, bursting the earth, threw it up into mountains and vallies. You ask me what I think of his book? I find in it many interesting facts brought together, and many ingenious commentaries on them. But there are great chasms in his facts, and consequently in his reasoning. These he fills up by suppositions which may be as reasonably denied as granted. A sceptical reader therefore, like myself, is left in the lurch. I acknolege however he makes more use of fact than any other writer of a theory of the earth. But I give one answer to all these theorists. That is as follows: they all suppose the earth a created existence. They must suppose a creator then; and that he possesed power and wisdom to a great degree. As he intended the earth for the habitation of animals and vegetables is it reasonable to suppose he made two jobs of his creation? That he first made a chaotic lump and set it into rotatory motion, and then waiting the millions of ages necessary to form itself, that when it had done this he stepped in a second time to create the animals and plants which were to inhabit it? As the hand of a creator is to be called in, it may as well be called in at one stage of the process as another. We may as well suppose he created the earth at once nearly in the state in which we see it, fit for the preservation of the beings he placed on it. But it is said we have a proof that he did not create it in it’s present solid form, but in a state of fluidity, because it’s present shape of an oblate spheroid is precisely that which a fluid mass revolving on it’s axis would assume. But I suppose that the same equilibrium between gravity and centrifugal force which would determine a fluid mass into the form of an oblate spheroid, would determine the wise creator of that mass, if he made it in a solid state, to give it the same spheroidical form. A revolving fluid will continue to change it’s shape till it attains that in which it’s principles of contrary motion are balanced; for if you suppose them not balanced, it will change it’s form. Now the same balanced form is necessary for the preservation of a revolving solid. The creator therefore of a revolving solid would make it an oblate spheroid, that figure alone admitting a perfect equilibrium. He would make it in that form for another reason, that is, to prevent a shifting of the axis of rotation. Had he created the earth perfectly spherical, it’s axis might have been perpetually shifting by the influence of other bodies of the system, and by placing the inhabitants of the earth successively under it’s poles, it might have been depopulated: whereas being Spheroidical it has but one axis on which it can revolve in equilibrio. Suppose the axis of the earth to shift 45.° Then cut it into 180 slices, making every section in the plane of a circle of latitude, perpendicular to the axis. Every one of these slices, except the equatorial one would be unbalanced, as there would be more matter on one side of it’s axis than on the other. There could be but one diameter drawn through such a slice which would divide it into two equal parts. On every other possible diameter the parts would hang unequal. This would produce an irregularity in the diurnal rotation. We may therefore conclude it impossible for the poles of the earth to shift, if it was made spheroidically, and that it would be made spheroidal, tho’ solid, to obtain this end. I use this reasoning only on the supposition that the earth has had a beginning. I am sure I shall read your conjectures on this subject with great pleasure, tho’ I bespeak before hand a right to indulge my natural incredulity and scepticism. The pain in which I write awakens me here from my reverie and obliges me to conclude with compliments to Mrs. Thomson, and assurances to yourself of the esteem and affection with which I am sincerely Dear Sir your friend & servt.,
P.S. Since writing the preceding, I have had conversation on the subject of the steam mills with the famous Boulton, to whom those of London belong, and who is here at this time. He compares the effect of steam with that of horses in the following manner. 6 horses, aided with the most advantageous combination of the mechanical powers hitherto tried, will grind six bushels of flour in an hour; at the end of which time they are all in a foam, and must rest. They can work thus 6. hours in the 24, grinding 36. bushels of flour, which is 6. to each horse for the 24 hours. His steam mill in London consumes 120 bushels of coal in 24 hours, turns 10. pr. of stones, which grind 8 bushels of flour an hour each, which is 1920 bushels for the 24. hours. This makes a peck and a half of coal perform exactly as much as a horse in one day can perform.