288 THE POPULAR SCIENCE MONTHLY. 



have been observed, I will merely call attention to the fact that in no 

 case have I heard any attending the reports of the rockets, 1 although 

 they seem to have been invariable with the guns and pistols. These 

 facts suggest that the echoes are in some way connected with the 

 direction given to the sound. They are caused by the voice, trump- 

 ets, and the siren, all of which give direction to the sound ; but I am 

 not aware that they have ever been observed in the case of a sound 

 which has no direction of greatest intensity." 



The reference to the voice and other references cause me to think 

 that, in speaking of echoes, Prof. Osborne Reynolds and myself are 

 dealing with different phenomena. Be that as it may, the foregoing 

 observations render it perfectly certain that the condition as to direc- 

 tion here laid down is not necessary to the production of the echoes. 



There is not a feature connected with the aerial echoes which can- 

 not be brought out by experiments in the laboratory. I have recent- 

 ly made the following experiment : A rectangle, 22 inches by 12, is 

 crossed by 23 brass tubes, each having a slit along it from which gas 

 can issue. In this way, 23 low, flat flames are obtained. A sounding 

 reed, fixed in a short tube, is placed at one end of the rectangle, and a 

 sensitive flame at some distance beyond the other end. When the reed 

 sounds, the flame in front of it is violently agitated, and roars boister- 

 ously. Turning on the gas, and lighting it as it issues from the slits, 

 the air above the flames becomes so heterogeneous that the sensitive 

 flame is instantly stilled by the aerial reflection, rising from a height of 

 6 inches to a height of 18 inches. Here we have the acoustic opacity 

 of the air in front of the South Foreland strikingly imitated. Turning 

 off the gas, and removing the sensitive flame to some distance behind 

 the reed, it burns there tranquilly, though the reed may be sounding. 

 Again lighting the gas as it issues from the brass tubes, the sound 

 reflected from the heterogeneous air throws the sensitive flame into 

 violent agitation. Here we have imitated the aerial echoes heard when 

 standing behind the siren-trumpets at the South Foreland. The ex- 

 periment is extremely simple, and in the highest degree impressive. 



-- 



WATER-SUPPLY OF RIYERS. 



By GEOEGE CHAHOON. 



IN the year 1871, three kilns were built on lot 54, Jay Tract, town 

 of Wilmington, Essex County, New York, for the purpose of burn- 

 ing wood into charcoal, to be used in making iron in the Catalan forges, 

 on the Ausable River. At the time these kilns were built, the side of 

 the mountain upon which they are located was covered with a heavy 



1 These earned 12 ounces of gunpowder. 



