CETAP. 1.] 



SOUND-SIGNALS. 



109 



Jugglers and others have not omitted to make use of this power 

 of transmitting sound to a distance. M. Eadau, in his Acoustics, 

 quotes several amusing examples of these applications ; the following 

 is one we borrow from him : 



"The invisible woman, who, at the beginning of this century, 

 excited such a great sensation in the principal towns of the Continent, 

 is explained in a very simple way. The most obvious part of this 

 machine (Fig. 65) was a hollow globe, fitted with four appendages in 

 the form of trumpets, and suspended freely from the ceiling of a 



FK;. <'>">. The invisible woman. 



room, by four silk bands. This sphere was surrounded with a trellis- 

 work cage, supported by four pillars, one of which was hollow and 

 communicated with the ground. The acoustic tube which passed 

 through it opened at the centre of one of the upper horizontal cross- 

 pieces, where there was a very narrow slit, scarcely perceptible to the 

 eye, opposite the orifice of one of the four trumpets. The voice 

 seemed then to issue from the sphere. It is possible that the person 

 who stood close at hand, and who gave the answers, was able to see 

 through a slit in the wall all that passed in the room. The questions 

 were asked through the orifice of one of the trumpets." 



