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tions were most exact and true, to wit, that sound traverses one mile in 9 1/4 half seconds; two miles in 18 1/2 seconds, three miles in 27 3/4 half seconds, and so on.
8. Concerning the upward and downward motion of sounds, or concerning the ascent and descent of sounds. Likewise whether they pass from place to place in a straight line or according to the superficies of the intervening land.
As regards questions 15 and 19, I frankly confess that I have never satisfied myself on these points by any of the experiments which I have hitherto made. In the first place let us treat the progress of sound by the shortest path, under the head of question 19. The reason for doubt about this was the discrepancy between the distance from Weal to Upminster by trigonometrical measurement and by sound, as is exhibited in the preceding table. The trigonometrical measurement was taken in so many ways and with such good angles, that I can have no doubt about it. But since the distance as meas- ured by the motion of sound seems to be greater, and since the superficies of the intervening ground takes on a form like that exhibited in this figure,
I have in consequence, somewhat doubted whether sound may or may not move a little crookedly, that is, whether or not that intervening elevation at “A”, by the resist- ance which it offers to the mass of sound beats them back and retards them.
That I might in some way solve this problem I took care that experiments should be made with the sound of a musket from the top of Langdon hill to the valley below at a distance of 3.79 miles. The distance was well measured trigonometri- cally, from angles and from a base line sufficiently large; and the experiment was made while a gentle breeze was slightly opposing the sound. Between the flash and the report I counted 35 1/2 half seconds. This number squares so exactly with the distance, and so nearly agrees with other experi- ments that it cannot be doubted that the sound descended from the top into the valley by a straight line (through the air), and not according to the curved superficies of the inter- vening ground.
I believe therefore that there was some error in the afore- said observations at Weal since neither in the last experiment at Langdon, nor in any others, have I observed anything like it.
As regards the upward and downward motion of sound, that is, whether sounds are borne with equal tenor and at the same rate from the top of a mountain to the bottom, I scarcely hope that I shall ever satisfy myself or any body else. For neither in Essex nor in the conterminous parts are any hills found high enough from which one may make sufficient experiments to this end. In fact the highest of all which it has yet been my lot to see, (such as those which they call the Langdon hills), do not much exceed 300 ft. For I measured the highest of these hills both by trigonometry and by a portable barometer, and I found it to be by the former mode 363 ft high by the latter mode, ... [ellipsis in Latin manuscript.]
On a former summer, however, when I was making a journey in the western parts of the kingdom, I determined to try an experiment on a certain hill whose altitude I ascer- tained by measurement a few years previously to be (unless
my memory deceives me) about 1875 feet. At a time when the wind was blowing across the path of the sound, but so gently that it would not extinguish a lighted candle, I ordered some muskets to be discharged at the base and at the top of the mountains, and I perceived that the sound reached me from each in almost the same interval of time. If I observed any slight discrepancy at all it seemed to consist in this that the sound may have ascended somewhat more swiftly towards the mountain than it descended from the mountain. But to speak according to the fact, I was scarcely able to measure the time with the accuracy which is due, since unluckily, it had turned out that the chronometer which I used had been somewhat disturbed by a concussion received on the journey.
Hence I leave this experiment to be tried more success- fully and certainly by others. And I would that the votaries of higher culture and philosophy among the Italians, (in whom has been implanted a curious felicity of genius) might be will- ing to try this same experiment on the Alps.
9. Concerning the translation or motion of sound in Italy.
Inasmuch as I have made mention of the Italians, it seems not irrelevant to recite certain observations and exper- iments made in Italy on my account by that very acute, learned and accomplished friend of mine Dr. Newton, the envoy of her Britannic Majesty at Florence. [This Dr. Newton is Henry Newton, not Isaac Newton. Both Newtons were Fellows of the Royal Society.] The occasion of these was as follows:
The late ingenious and excellent Richard Towneley, Esq., (a name familiar and grateful to our renowned society) had signified to me by a letter written in the year 1704, that “Sounds are rarely heard as far at Rome as in England and in our northern regions.” He said particularly that while he was staying at Rome, on an occasion when some cannon of the castle of St. Angelo were fired on account of joyous intelli- gence, and when he was standing on Mount Trinita, he has observed that the sound was much more languid in that situ- ation than in any other location at the same distance. And after the death of Towneley [The name does not appear in the Latin manuscript. Welling inserts Newton’s name here by mistake. The reference is to the late Richard Towneley. Henry Newton is still alive when Derham writes this paper (see the next paragraph)], his brother reported to me, in writ- ing, that in the year 1688, “when on leaving Rome, he repaired, for a season of recreation to Castel Gandolfo (a cer- tain higher location near Lake Albano, about 13 Italian miles from Rome), he had observed that the sound of the heavy cannon booming from the aforesaid Castle of St. Angelo seemed to him reduced in volume and weak. Also at another time when he was passing around the walls of this same cas- tle in a carriage, and when the great guns were bellowing from it, they seemed to send forth a sound which, as there observed, was neither in quality nor volume like that observed elsewhere.”
Since these things had been noticed by two men of no common intellect, and since the phenomenon itself seemed entirely new and unusual, the desire entered my mind of enquiring what might be the cause of it. I therefore wrote to
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