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representatives. The ministry seemed to view the matter in the same light, for the money was paid to the agent of the Assembly.
Having now finished the most important parts of his public business, he had leisure for other employments. In the summer of 1761, he went over to the continent, and travelled through Holland and Flanders, visiting the large cities, and returning in time to be present at the coronation of George the Third. There is no record of the incidents of this tour, except a short letter to his wife written at Utrecht, in which he says, he "had seen almost all the principal places, and the things worthy of notice, in those two countries, and received a good deal of information, that would be useful when he returned to America."
His philosophical studies had been in a measure suspended for some time; yet he had recurred to them occasionally, and performed experiments, which were attended with novel or useful results. There was a dispute among the philosophers about the properties of tourmalin, a stone which pinus had discovered to possess the singular quality of being at the same time positively electrified on one side, and negatively on the opposite side, by heat alone, without the aid of friction. Others denied this fact. Franklin made a series of experiments with two specimens of tourmalin, given to him by Dr. Heberden, which confirmed Epinus's account. He found, that the heat of boiling water was sufficient to excite these opposite electrical properties, and he supposed that others had failed in the experiment by using imperfect stones, or such as had not their faces properly cut.
Before he left America, Professor Simson, of Glasgow, had communicated to him some curious experiments made by Dr. Cullen, showing that cold could
be produced by evaporation. This fact, so well established since, was then little known. He repeated the experiment, by applying spirits of wine to the bulb of a thermometer, and thereby caused the mercury to fall five or six degrees. On his first visit to the University of Cambridge, at the suggestion of Dr. Hadley, professor of chemistry there, he performed the same process with ether, when the mercury fell to twentyfive degrees below the freezing point, and ice was formed on the bulb to the thickness of a quarter of an inch. "From this experiment," he observes, "one may see the possibility of freezing a man to death on a warm summer's day, if he were to stand in a passage through which the wind blew briskly, and to be wet frequently with ether, a spirit more inflammable than brandy or common spirits of wine."
This principle of evaporation he applied to an ingenious solution of several phenomena, hitherto unconsidered or unexplained. Among others, it furnished him with a reason why the heat of the human body is not increased above its natural temperature, or ninetysix degrees, by hot air, while inanimate substances will receive an accumulation of heat. He had himself known the thermometer to stand at one hundred degrees in the shade at Philadelphia, while the heat of his body was not above its usual temperature of ninetysix. Being at the same time in a profuse perspiration, he inferred, that the heat was carried off by evaporation, as fast as it came in contact with his body from the surrounding air. Hence, laborers in the harvest field, under a burning sun, will endure excessive heat, whilst they perspire freely, and drink a sufficient quantity of water, or other liquid, to supply the moisture that is exhausted by evaporation.
His mind was ever busy in searching for the causes
not only of remarkable phenomena, but of the common operations of nature. A visit to the salt-mines in England led him to reflect on the formation of those mines and on the saltness of the sea. "It has been the opinion of some great naturalists," he observes, "that the sea is salt only from the dissolution of mineral or rock salt, which its waters happened to meet with. But this opinion takes it for granted, that all water was originally fresh, of which we can have no proof. I own I am inclined to a different opinion, and rather think all the water on this globe was originally salt, and that the fresh water we find in springs and rivers, is the produce of distillation. The sun raises the vapors from the sea, which form clouds, and fall in rain upon the land, and springs and rivers are formed of that rain. As to the rock salt found in mines, I conceive, that, instead of communicating its saltness to the sea, it is itself drawn from the sea, and that of course the sea is now fresher than it was originally. This is only another effect of nature's distillery, and might be performed various ways." One of these ways he thus describes. "As we know from their effects, that there are deep fiery caverns under the earth, and even under the sea, if at any time the sea leaks into any of them, the fluid parts of the water must evaporate from that heat, and pass off through some volcano, while the salt remains, and by degrees, and continual accretion, becomes a great mass. Thus the cavern may at length be filled, and the volcano connected with it cease burning, as many, it is said, have done; and future miners, penetrating such cavern, find what we call a salt-mine." This may be no more than a theory, but perhaps it is as good a theory as any other that has been advanced on the subject.
To Mr. Alexander Small, a gentleman in London
fond of scientific inquiries, he communicated his reason for thinking that the northeast storms, so common along the Atlantic coast of North America, extending from Newfoundland to Florida, begin at the southeast. In October, 1743, there was to be an eclipse of the moon at nine o'clock in the evening, which he prepared to observe at Philadelphia. But when the time came, the heavens were overcast, and a northeast storm had set in. He was surprised to learn, therefore, by the Boston newspapers, that the eclipse was visible in a clear sky at that place, as he' supposed a storm, attended by a strong wind from that quarter, would naturally begin there first. He ascertained, however, that it actually began in Boston nearly four hours later than in Philadelphia, and that along the southern coast it began earlier in proportion as any given place was less distant from the Gulf of Mexico. This put him upon observing these storms whenever they occurred; and he found in each instance, that they began at the southeast, and moved northwestward, against the current of the wind, at the rate of about one hundred miles an hour.
The fact being established, he next set himself to assign a reason. Experience shows, that cool air will flow in and occupy the place of warmer and more rarefied air. A fire in a chimney is made to burn, and the smoke and warm air to ascend, by a current of air flowing into it from the room. The motion begins at the chimney, where a portion of air is first displaced, and thus a current is produced from all parts of the room towards the chimney. For several days previously to one of these storms, he supposes the air to become heated and rarefied by the rays of the sun about the regions of the Gulf of Mexico and Florida. The cooler and moister air from the northeast flows
in and causes the rarefied air to ascend; clouds and rain are formed by the action of heat upon this cooler and moister air; and thus the storm begins, with a current of wind setting from the northeast. The denser air presses upon the lighter, till the current extends itself, in a retrograde direction, along the whole coast.*
From early life he had a passion for music, and he both studied it as a science, and practised it as an art. His remarks on the harmony and melody of the old Scotch songs have been much commended. Mr. Tytler says, "This notion of Dr. Franklin's, respecting what may be called the ideal harmony of the Scottish melodies, is extremely acute, and is marked by that ingenious simplicity of thought, which is the characteristic of a truly philosophical mind." In a letter to his brother he explains the defects of modern music, with the same simplicity and acuteness, illustrating his idea by a criticism on one of Handel's admired compositions. ‡
In London he saw for the first time an instrument, consisting of musical glasses, upon which tunes were played by passing a wet finger round their brims. He was charmed with the sweetness of its tones; but the instrument itself seemed to him an imperfect contrivance, occupying much space and limited in the number of its tones. The glasses were arranged on a table, and tuned by putting water into them till they gave the notes required.
After many trials he succeeded in constructing an instrument of a different form, more commodious, and
*The facts and hypothesis, respecting northeast storms, are likewise contained in a letter written to the Reverend Jared Eliot, ten years before they were communicated to Mr. Small, which is now for the first time published in this work. See Vol. VI. p. 105.
+ Life of Lord Kames, 2d ed. Vol. II. p. 31. See Vol. VI. p. 269.