M. C. Sondhauss on the Refraction of Sound. 75 



the sonorous waves whicli were generated by the ticking of a 

 watch. The watch was placed at the same height as the centre 

 of the lens, and the latter received upon its membranous surface 

 the waves proceeding from the watch, and transmitted them 

 through the carbonic acid to the air at the other side. In 

 repeated experiments it was found that the ticking of the watch 

 was distinctly audible at a point in the axis of the lens, while 

 out of the axis, at an equal or even less distance, the ticking was 

 either less audible or not at all to be heard. Inasmuch as a 

 subjective error might readily creep into such experiments, I 

 have not relied upon the judgement of my own ear alone, but 

 have subjected the experiment to the judgement of others, who 

 all found the phsenomenon to be exactly as I have stated it. I 

 can here call upon the testimony of such observers as Bunsen, 

 Duflos, Frankenheim, Gebauer and Kirchhof, who have all been 

 kind enough to attend my experiments. To arrive at a certain 

 decision, the experiment was so modified, that, while the observer 

 sat with closed eyes at one side of the lens and listened to the 

 ticking of the watch at the other, the lens was alternately removed 

 and brought into its place. It was thus found that the ticking 

 ceased every time the lens was withdrawn, and immediately 

 heard again as soon as the lens was replaced between the watch 

 and the observer. When the hand was held before the watch so 

 as to intercept the sonorous waves and prevent them from falling 

 on the lens, the ticking was not heard, but was immediately 

 audible when the hand was removed. 



It would have been very interesting to me to determine the 

 distance of the point of convergence of the rays of sound corre- 

 sponding to different distances between the watch and the lens. 

 The ear, however, is not suited to observations of this character ; 

 and I have scarcely ever been able to decide at what distance 

 from the lens the ticking of the watch was loudest. The greater 

 or less attention, the wearying of the observer, the irregular 

 stroke of the watch, and the circumstance that in the neighbour- 

 hood the same tranquillity does not always reign, are sources of 

 perpetual error in these observations ; T will therefore for the 

 present merely state generally, that the place where the ticking 

 of the watch appeared to be most plainly heard moved to a greater 

 distance from the lens when the watch was brought closer to the 

 latter, and will introduce merely a single series of observations, 

 in which I have endeavoured to determine to what distance 

 behind the lens the ticking could be heard, when the watch was 

 suspended at various distances. 



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