Another important point is, that Watt and Cavendish's papers on the discovery were printed under the sole superintendence of Dr. Blagden, secretary to the Royal Society; that Mr. Watt's paper is printed with the erroneous date of 1784, in place of 1783, and that the separate copies of Mr. Cavendish's papers have the erroneous date of 1783, in place of 1784. The obvious effect of these two errors was to give Cavendish the priority over Watt; whereas, by written testimony, Watt's theory is proved to have been known to Priestley in 1782.
It is Dr. Blagden's conduct in the matter that has disturbed the current of scientific history. "It is his testimony," says an able writer in the North British Review, "not appealed to by Cavendish, but gratuitously offered by himself, that contains the allegation that Cavendish mentioned to him and others his conclusions. It is his testimony, gratuitously sent to Crell, that deprives the French chemists, Lavoisier, Laplace, and Monge, of their due share of honour; and it was by his acts that erroneous dates and claims were propagated throughout Europe. Let us impanel, then, a British jury—not of chemists, for their verdict is given—not of the improvers or manufacturers of steam-engines, for they might be partial—but of the highest functionaries of the law, the members of the peerage—let us lay before them these facts, and then tell them that Blagden received an annuity of 500l. from Cavendish; that, at his death, he left him a legacy of 15,000l.; and we will answer for it, that the testimony of Blagden will be rejected, and the priority of Watt affirmed."
HOW PASCAL WEIGHED THE ATMOSPHERE.
Pascal's Treatise on the weight of the whole mass of air forms the basis of the modern science of Pneumatics. In order to prove that the mass of air presses by its weight on all the bodies which it surrounds, and also that it is elastic and compressible, he carried a balloon, half filled with air, to the top of the Puy de Dome, a mountain about 500 toises above Clermont, in Auvergne. It gradually inflated itself as it ascended, and when it reached the summit, it was quite full, and swollen as if fresh air had been blown into it; or, what is the same thing, it swelled in proportion as the weight of the column of air which pressed upon it was diminished. When again brought down, it became more and more flaccid, and when it reached the bottom, it resumed its original condition. In the nine chapters of which the Treatise consists, Pascal shows that all the phenomena and effects hitherto ascribed to the horror of a vacuum arise from the weight of the mass of air; and after explaining the variable pressure of the atmosphere in different localities, and in its different states, and the rise of water in pumps, he calculates that the whole mass of air round our globe weighs 8,983,889,440,000,000,000 French pounds.
THE LEANING TOWER OF PISA.[[2]]
Sir John Leslie used to attribute the stability of this tower to the cohesion of the mortar it is built with being sufficient to maintain it erect, in spite of its being out of the condition required by physics—to wit, that "in order that a column shall stand, a perpendicular let fall from the centre of gravity must fall within the base." Sir John describes the column of Pisa to be in violation of this principle; but, according to designs shown to Dr. Cumming, at Pisa, in 1836, the perpendicular does fall within the base.
| [2] | When at Pisa, many years since, Captain Basil Hall investigated the origin and divergence of the tower from the perpendicular, and established completely to his own satisfaction that it had been built from top to bottom, originally, just as it now stands. His reasons for thinking so are, that the line of the tower, on that side towards which it leans, has not the same curvature as the line on the opposite, or what may be called the upper side. If the tower had been built upright, and then been made to incline over, the line of the wall on that side towards which the inclination was given, would be more or less concave in that direction, owing to the nodding or "swagging over" of the top, by the simple action of gravity acting on a very tall mass of masonry, which is more or less elastic when placed in a sloping position. But the contrary is the fact; for the line of wall on the side towards which the tower leans, is decidedly more convex than the opposite side. Captain Hall has, therefore, no doubt whatever that the architect, in rearing his successive courses of stones, gained or stole a little at each layer, so as to render his work less and less overhanging as he went up; and thus, without betraying what he was about, really gained stability. |