42 BULLETIN OF THE 



miles, as well as the primary sound, or even better than the latter. 

 He observes that echoes produced by the firing of cannon on the 

 Thames river, between Deptford and Cuckold's Point, came to his 

 ears in a multiple form, repeated five or six times, and the terminal 

 crash of the echo was the loudest. This last feature was observed 

 even when the multiple sounds were nine or ten in number. To 

 this he adds : " When I have heard the crashes of heavy artillery, 

 especially in a still and clear atmosphere, I«have often observed that 

 a murmur high in the air preceded the report. And in thin fog 

 I have often heard the sound of cannon running in the air, high 

 above my head, through many miles, so that this murmur has lasted 

 fifteen seconds. This continuous murmur, in my opinion, comes 

 from particles of vapor suspended in the atmosphere which resist 

 the course of the sound waves, and reverberate them back to the 

 ears of the observer after the manner of undefined echoes.* 



Mr. Richard Townley, an intelligent observer, having written to 

 Dr. Derham, in a letter from Rome, that " sounds are rarely heard 

 as far at Rome as in England and in other northern regions, and 

 having cited in support of this statement some observations drawn 

 from the firing of cannon in the castle of St. Angelo, Dr. Derham 

 caused an enquiry on this point to be made in Italy, under the aus- 

 pices of the British Minister at Florence. The enquiry was con- 

 ducted by Joseph Averani, a Professor in the University of Pisa. 

 Guns were fired at Florence, and observers were stationed at differ- 

 ent points in Leghorn and its vicinity to mark the effect of the 

 reports. The observers stationed in the Light-House and the Mar- 

 zocco tower, in the lower part of the city, heard no reports, but ob- 

 servers stationed on an old fortress in the upper part of the city? 

 and other observers placed on Monte Rotondo, about five miles 

 from Leghorn in the direction of Mount Nero, (and, therefore, more 

 in the direction of the wind which was blowing across the path of 

 the sound,) were able to hear the reports. 



Another series of experiments was made on water, by firing 

 cannon at Leghorn, and stationing observers at Porto Ferrajo 

 in the Island of Elba, a distance of about sixty miles. In this 

 case the reports were better heard in still air than when the wind 

 was either favorable or unfavorable, and were not heard at all 

 points equally well, but only at those which were a little the more 

 elevated .f 



* Derham, p. 10. f Ibid., pp. 18, 19, 20. 



