James Watt by Andrew Carnegie (english reading book TXT) 📕

Watt, to whom Priestley communicated this important result, immediately perceived that proof was here afforded that water was not a simple body. Writing to his illustrious friend, he asks:

What are the products of your experiment? They are water, light and heat. Are we not, thence, authorised to conclude that water is a compound of the two gases, oxygen and hydrogen, deprived of a portion of their latent or elementary heat; that oxygen is water deprived of its hydrogen, but still united to its latent heat and light? If light be only a modification of heat, or a simple circumstance of its manifestation, or a component part of hydrogen, oxygen gas will be water deprived of its hydrogen, but combined with latent heat.

This passage, so clear, so precise, and logical, is taken from a letter of Watt's, dated April 26, 1783. The letter was communicated by Priestley to several of the scientific men in London, and was transmitted immediately afterward to Sir Joseph Banks, the President of the Royal Society, to be read at one of the meetings of that learned body.

Watt had for many years entertained the opinion that air was a modification of water. He writes Boulton, December 10, 1782:

You may remember that I have often said, that if water could be heated red-hot or something more, it would probably be converted into some kind of air, because steam would in that case have lost all its latent heat, and that it would have been turned solely into sensible heat, and probably a total change of the nature of the fluid would ensue.

A month after he hears of Priestley's experiments, he writes Dr. Black (April 21, 1783) that he "believes he has found out the cause of the conversion of water into air." A few days later, he writes to Dr. Priestley:

In the deflagration of the inflammable and dephlogisticated airs, the airs unite with violence—become red-hot—and, on cooling, totally disappear. The only fixed matter which remains is water; and water, light, and heat, are all the products. Are we not then authorised to conclude that water is composed of dephlogisticated and inflammable air, or phlogiston, deprived of part of their latent heat; and that dephlogisticated, or pure air, is composed of water deprived of its phlogiston, and united to heat and light; and if light be only a modification of heat, or a component part of phlogiston, then pure air consists of water deprived of its phlogiston and of latent heat?

It appears from the letter to Dr. Black of April 21st, that Mr. Watt had, on that day, written his letter to Dr. Priestley, to be read by him to the Royal Society, but on the 26th he informs Mr. DeLuc, that having observed some inaccuracies of style in that letter, he had removed them, and would send the Doctor a corrected copy in a day or two, which he accordingly did on the 28th; the corrected letter (the same that was afterward embodied verbatim in the letter to Mr. DeLuc, printed in the Philosophical Transactions), being dated April 26th. In enclosing it, Mr. Watt adds, "As to myself, the more I consider what I have said, I am the more satisfied with it, as I find none of the facts repugnant."

Thus was announced for the first time one of the most wonderful discoveries recorded in the history of science, startling in its novelty and yet so simple.

Watt had divined the import of Priestley's experiment, for he had mastered all knowledge bearing upon the question, but even when this was communicated to Priestley, he could not accept it, and, after making new experiments, he writes Watt, April 29, 1783, "Behold with surprise and indignation the figure of an apparatus that has utterly ruined your beautiful hypothesis," giving a rough sketch with his pen of the apparatus employed. Mark the promptitude of the master who had deciphered the message which the experimenter himself could not translate. He immediately writes in reply May 2, 1783:

I deny that your experiment ruins my hypothesis. It is not founded on so brittle a basis as an earthen retort, nor on its converting water into air. I founded it on the other facts, and was obliged to stretch it a good deal before it would fit this experiment.... I maintain my hypothesis until it shall be shown that the water formed after the explosion of the pure and inflammable airs, has some other origin.

He also writes to Mr. DeLuc on May 18th:

I do not see Dr. Priestley's experiment in the same light that he does. It does not disprove my theory.... My assertion was simply, that air (i.e., dephlogisticated air, or oxygen, which was also commonly called vital air, pure air, or simple air) was water deprived of its phlogiston, and united to heat, which I grounded on the decomposition of air by inflammation with inflammable air, the residuum, or product of which, is only water and heat.

Having, by experiments of his own, fully satisfied himself of the correctness of his theory, in November he prepared a full statement for the Royal Society, having asked the society to withhold his first paper until he could prove it for himself by experiment. He never doubted its correctness, but some members of the society advised that it had better be supported by facts.

When the discovery was so daring that Priestley, who made the experiments, could not believe it and had to be convinced by Watt of its correctness, there seems little room left for other claimants, nor for doubt as to whom is due the credit of the revelation.

Watt encountered the difficulties of different weights and measures in his studies of foreign writers upon chemistry, a serious inconvenience which still remains with us.

He wrote Mr. Kirwan, November, 1783:

I had a great deal of trouble in reducing the weights and measures to speak the same language; and many of the German experiments become still more difficult from their using different weights and different divisions of them in different parts of that empire. It is therefore a very desirable thing to have these difficulties removed, and to get all philosophers to use pounds divided in the same manner, and I flatter myself that may be accomplished if you, Dr. Priestley, and a few of the French experimenters will agree to it; for the utility is so evident, that every thinking person must immediately be convinced of it.

Here follows his plan: Let the

Philosophical pound consist of 10 ounces, or 10,000 grains.
the ounce    "    "  10 drachms or 1,000    "
the drachm  "    "  100 grains.

Let all elastic fluids be measured by the ounce measure of water, by which the valuation of different cubic inches will be avoided, and the common decimal tables of specific gravities will immediately give the weights of those elastic fluids.

If all philosophers cannot agree on one pound or one grain, let every one take his own pound or his own grain; it will affect nothing but doses of medicines, which must be corrected as is now done; but as it would be much better that the identical pound was used by all. I would propose that the Amsterdam or Paris pound be assumed as the standard, being now the most universal in Europe: it is to our avoirdupois pound as 109 is to 100. Our avoirdupois pound contains 7,000 of our grains, and the Paris pound 7,630 of our grains, but it contains 9,376 Paris grains, so that the division into 10,000 would very little affect the Paris grain. I prefer dividing the pound afresh to beginning with the Paris grain, because I believe the pound is very general, but the grain local.

Dr. Priestley has agreed to this proposal, and has referred it to you to fix upon the pound if you otherwise approve of it. I shall be happy to have your opinion of it as soon as convenient, and to concert with you the means of making it universal.... I have some hopes that the foot may be fixed by the pendulum and a measure of water, and a pound derived from that; but in the interim let us at least assume a proper division, which from the nature of it must be intelligible as long as decimal arithmetic is used.

He afterward wrote, in a letter to Magellan:

As to the precise foot or pound, I do not look upon it to be very material, in chemistry at least. Either the common English foot may be adopted according to your proposal, which has the advantage that a cubic foot is exactly 1,000 ounces, consequently the present foot and ounce would be retained; or a pendulum which vibrates 100 times a minute may be adopted for the standard, which would make the foot 14.2 of our present inches, and the cubic foot would be very exactly a bushel, and would weigh 101 of the present pounds, so that the present pound would not be much altered. But I think that by this scheme the foot would be too large, and that the inconvenience of changing all the foot measures and things depending on them, would be much greater than changing all the pounds, bushels, gallons, etc. I therefore give the preference to those plans which retain the foot and ounce.

The war of the standards still rages—metric, or decimal, or no change. What each nation has is good enough for it in the opinion of many of its people. Some day an international commission will doubtless assemble to bring order out of chaos. As far as the English-speaking race is concerned, it seems that a decided improvement could readily be affected with very trifling, indeed scarcely perceptible, changes. Especially is this so with money values. Britain could merge her system with those of Canada and America, by simply making her "pound" the exact value of the American five dollars, it being now only ten pence less; her silver coinage one and two shillings equal to quarter- and half-dollars, the present coin to be recoined upon presentation, but meanwhile to pass current. Weights and measures are more difficult to assimilate. Science being world-wide, and knowing no divisions, should use uniform terms. Alas! at the distance of nearly a century and a half we seem no nearer the prospect of a system of universal weights and measures than in Watt's day, but Watt's idea is not to be lost sight of for all that. He was a seer who often saw what was to come.

We have referred to the absence of holidays in Watt's strenuous life, but Birmingham was remarkable for a number of choice spirits who formed the celebrated Lunar Society, whose members were all devoted to the pursuit of knowledge and mutually agreeable to one another. Besides Watt and Boulton, there were Dr. Priestley, discoverer of oxygen gas, Dr. Darwin, Dr. Withering, Mr. Keir, Mr. Galton, Mr. Wedgwood of Wedgwood ware fame, who had monthly dinners at their respective houses—hence the "Lunar" Society. Dr. Priestley, discoverer of oxygen, who arrived in Birmingham in 1780, has repeatedly mentioned the great pleasure he had in having Watt for a neighbor. He says:

I consider my settlement at Birmingham as the happiest event in my life; being highly favourable to every object I had in view, philosophical or theological. In the former respect I had the convenience of good workmen of every kind, and the society of persons eminent for their knowledge of chemistry; particularly Mr. Watt, Mr. Keir, and Dr. Withering. These, with Mr. Boulton and Dr. Darwin, who soon left us by removing from Lichfield to Derby, Mr. Galton, and afterwards Mr. Johnson of Kenilworth and myself, dined together every month, calling ourselves the Lunar Society, because the time of our meeting was near the full-moon—in order,

as he elsewhere says,

to have the benefit of