Page 34 - January 2009

my many experiments. And what I have just now suggested respecting the sound of the artillery on Blackheath, I have found in all other cases, viz. that the motion of sound is nei- ther swifter nor slower whether the cannon be fired towards the observer or in the opposite direction.
Likewise, in all positions of a musket, whether horizon- tal or perpendicular, and at all elevations, ten degrees, twen- ty degrees, etc., there is no variation in the sound of its dis- charge. So true in this matter is the observation of those famous gentlemen connected with the Accademi del Cimento in Florence.
The force also of the powder, whether it be strong or weak, and the greater or less the quantity of the charge, though serving to increase or diminish the sound, have no effect in accelerating or retarding its motion.
5. Concerning the velocity of sound in any state of the atmosphere and any time of the year.
Kircher [Athanasius Kircher (1602-1680), a German Jesuit scholar] says, that he always found the velocity of sound to be different at different times, at morning, at midday, at evening and at night. But I, relying on a better chronometer and using a more suitable distance, never have found that the celerity of sound is different at these times, but in all weather, whether the atmosphere be clear and serene, or cloudy and turbid; whether snow is falling or fog, (which both powerfully blunt the audibil- ity of sound) [This generalization is, unfortunately, one of Derham’s remarks that influenced thought for about 150 years. Subsequent descriptions by Derham in Section 10 indicate that he was really not unequivocal in this opinion and he may have succumbed to repeating popular lore here.]; whether it thunders or it lightnings, whether heat or cold dries the air; whether it be day or night, summer or winter; whether the mercury is rising or falling in the barometer—in a word I may say that in all changes of atmosphere whatsoever (winds only being excepted) the velocity of sound is neither greater nor less. [The one impor- tant factor that Derham missed was the dependence of sound speed on temperature. Given the chronometers available to Derham at the time and the fact that the effects of wind are nor- mally considerably larger than the effects of temperature, it is not at all surprising that Derham did not see the change in sound speed with temperature. It would be almost half a centu- ry before Bianconi provided convincing experimental evidence of the temperature dependence of sound speed.] The sound is only more or less clear from this variation of the medium, and perhaps this fact deceives the sagacious Kircher.
Hence it follows that the conclusions drawn by Mr. Walker from his ingenious observations and from those of Dr. Plot (Derham note: Philos. Trans. N. 247.) and of Kircher were erro- neous. [The more complete reference is “Some Experiments and Observations concerning Sounds,” By Mr. Walker, Late of Brazen-Nose-College, Oxon. Philosophical Transactions (1683-1775), Vol. 20. (1698), pp. 433-438.]
6. Concerning the velocity of a strong and of a weak sound, and of the sound of different sounding bodies.
Though Kircher thinks otherwise I do not doubt that the sounds of all bodies—of muskets, bells, hammers, etc., have
the same velocity. In the year 1704, I compared the beatings of a hammer and the crack of a musket at the interval of a mile (the greatest distance at which I could hear the sound of a hammer), and I found that the sound of both reached me in the same time, as also that they traversed 3/4, 1/2 and 1/4 of the same space in 3/4, 1/2 and 1/4 of the same time.
As regards strong and weak sounds I do not doubt that they traverse the same space in the same interval of time. This fact will be in a measure apparent from the following experiments:
January 13, 1704: The master gunner of Tilbury Fort at my request fired two gun shots in succession, and a heavy cannon in which he had well measured a charge of powder. The report of all these reached me at the distance of about three miles in the same time.
The master gunner of England [Translator’s note: “The Master Gunner of England” was the title of the Senior Master Gunner in the ordinance service of England at this period.] also on the 11th Sept. 1705, after sunset, as a matter of favor to me fired on Blackheath some muskets, some heavy can- non, (Sakers) and some mortars. I could not hear the muskets on account of the great distance, or because the air was not sufficiently serene. But I heard the sounds of the cannon and of the mortars in the same interval of time, though the crash of the mortar was much more torpid and weak than that of the cannon.
Notwithstanding the fact that I used the greatest care in
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