278 FKAGMENTS OF SCIENCE. 



as they accompany the horizontal one. The experi- 

 ment, as I interpret it, is not opposed to the theory of 

 these echoes which I have ventured to enunciate. But, 

 as I have indicated, not only to see but to vary such 

 an experiment is a necessary prelude to grasping its 

 full significance. 



In a paper published in the f Philosophical Trans- 

 actions ' for 1876, Professor Osborne Eeynolds refers 

 to these echoes in the following terms: ' 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,* 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 Os- 

 borne Eeynolds and myself are dealing with different 

 phenomena. Be that as it may, the foregoing observa- 

 tions render it perfectly certain that the condition as 

 to direction here laid down is not necessary to the pro- 

 duction 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, x Y (p. 279), 22 

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

 (half the number would suffice and only eleven are 



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

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



