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



the direction of the axis, more plainly than at an equal or less 

 distance in any other direction ; the difference, however, did not 

 seem to me to be sufficiently considerable to furnish a conclusive 

 proof of the refraction of sound, or to justify the publication of 

 the experiment. I next endeavoured to obtain a membranous 

 convex lens instead of the balloon, and succeeded finally in con- 

 structing one of post-paper. I obtained, however, no result with 

 it, probably because the spherical paper surfaces were too stiff 

 to receive and transmit the weak undulations excited by the 

 ticking of the watch. 



Otherwise occupied, I let the experiment rest until after the 

 discovery of collodion. By the kindness of M. Miiller, apo- 

 thecary in Breslau, who exhibits great skill in the preparation of 

 collodion balloons, I was enabled to construct a large lens 

 which was suited to the experiments intended. M. Miiller 

 prepared for this purpose a gigantic balloon; out of it two 

 segments were cut and attached to a hoop of lead, so that 

 the lens-shaped body thus obtained consists, when blown out, of 

 a low cylinder, whose ends are spherical segments. The hoop 

 of lead has a diameter of eleven and a third Paris inches, and a 

 breadth of two and a quarter ; one of the two spherical segments 

 possesses a height of 2'' l'""5, the other a height of 2" 2'"*5. 



In order to fix this apparatus conveniently at two diametri- 

 cally opposite points of the hoop, two lead tubes are soldered 

 which serve as axes, and rest upon two wooden pillars, so that 

 the lens can be turned round a horizontal axis and thus easily 

 set in either a perpendicular or horizontal position ; by length- 

 ening or shortening the two wooden pillars the lens can be set 

 either higher or lower. In the 

 annexed woodcut the lens and its 

 supports are represented; at D 

 and E are two other lead tubes 

 soldered to the hoop, and made 

 use of to inflate the lens. I fill 

 it from below, connecting D by 

 means of an elastic tube with the 

 carbonic acid apparatus, and per- 

 mitting the air to issue through 

 the upper orifice E. When the 

 lens is completely inflated, and the air driven out by the carbonic 

 acid, the elastic tube is first removed from the under opening D 

 and the tube closed with a good cork ; the upper orifice is then 

 tightly closed. 



As no suitable unenclosed space was at my disposition, the 

 observations were made in a room. In the first place, I observed 



