278 FKAGMENTS OF SCIENCE. 



experiment is a necessary prelude to grasping its full 

 significance. 



In a paper published in the ' Philosophical Trans- 

 actions ' for 1876, Professor Osborne Reynolds refers 

 to these echoes in the following terms : c Without 

 attempting to explain the reverberations and echoes 

 which 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, trumpets, and the syren, 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 in his paper, cause me to think 

 that, in speaking of echoes, Professor 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 direction here 

 laid down is not necessary to the production of the 

 echoes. 



There is not a feature connected with the aerial 

 echoes which cannot be brought out by experiments in 

 the air of the laboratory. I have recently made the 

 following experiment : A rectangle, XT (p. 279), 22 

 inches by 12, was crossed by twenty-three brass tubes 

 (half the number would suffice and only eleven are 

 shown in the figure), each having a slit along it from 

 which gas can issue. In this way twenty-three low 

 flat flames were obtained. A sounding reed a fixed in a 



1 These carried 12 oz. of gunpowder, which has been found by 

 Col. Fraser to require an iron case to produce an effective explosion, 



