388 PHILOSOPHICAL TRANSACTIONS. [aNNO 1708. 



wind is quite still, or blows but very softly, when the air is clear, and the sea 

 calm; nor is it then heard indifferently in all places, but only where the situa- 

 tion happens to be a little higher than ordinary : such are the two forts, Stella 

 and Falcona, and a place called Mulini ; besides it is requisite, that the observer 

 be as attentive as possible, and be not disturbed with the least noise : and then 

 it is heard in the day time, as well as in the night, provided the atmosphere be 

 clear and calm ; only that the sound seems stronger and somewhat acuter in the 

 night, when there happens no noise, as is frequently the case in the day time. 

 Moreover, S. Averrani was credibly informed, that at the siege of Messina, the 

 report of the great guns reached the ears of the inhabitants of Augusta and 

 Syracuse, at almost 100 Italian miles; and likewise when the French besieged 

 Genoa, the firing of their guns was plainly heard as far as Monte Nero, up- 

 wards of 90 Italian miles. From these observations Averrani is apt to think, 

 there is no difference in this matter, between Italy and the northern climates. 



As to the other query, viz. whether a favourable or contrary wind, accelerate 

 or retard the sound.'' The experiments Averrani had hitherto tried were in- 

 sufficient to resolve it; only he gives an account of the following one, viz. a 

 culverine was brought upon the curtain of the lower bastion of Florence, and 

 planted with its muzzle towards Artemino, a palace of the grand duke of Tus- 

 cany, situated on a rising ground, and facing the west flank of the said bastion, 

 from which it is also distant about 12 miles: he chose a day to make the experi- 

 ment, when there was a pretty strong westerly wind, that the motion of the 

 sound might be repelled by the contrary wind. But all this was to no purpose; 

 for the evening was so calm, that there was hardly a breath of air: Averrani, 

 having left in this place some persons skilful in those matters, with proper 

 directions, retired to the palace of Artemino, and the culverine was several 

 times discharged, between the first and third hours of the night, and each time 

 he reckoned 4g seconds between the flash and the report ; he also caused some 

 guns to be discharged at Artemino, and between the flash and the report of 

 each explosion the persons above-mentioned only reckoned 48 seconds: whence 

 it appeared, that the sound moved swifter by a second from Artemino to 

 Florence, than from Florence to Artemino; yet he could not so far depend on 

 his observation, as to ascribe. this small difference of velocity, either to the con- 

 currence or resistance of the wind; because it might be owing to the observer, 

 who reckoned the vibrations of the pendulum ; for it must often happen, that 

 he cannot see the flash till the pendulum begin to vibrate, nor hear the sound 

 before the vibration is quite ended; so that his calculation is greater by one 

 vibration, than it should be, though the space be the same. 



As to the space sound passes over in any given time, it is not hitherto de- 



