190 



THE POPULAR SCIENCE MONTHLY. 



'c^-VVsSl 



smoking the mica. In this experiment the effect was observed by- 

 placing the .mica diaphragm against the ear, and also by listening 

 through a hearing-tube, one end of Avhich was closed by the dia- 

 phragm. The sound was found 

 to be more audible throuo^h the 

 free air when the ear was placed 

 as near to the lampblack sur- 

 face as it could be brought 

 without shading it. 



At the time of my commu- 

 nication to the American Asso- 

 ciation I had been unable to 

 satisfy myself that the sub- 

 stances which had become so- 

 norous under the direct influ- 

 ence of intermittent sunlight 

 were capable of reproducing 

 the sounds of articulate speech 

 under the action of an undu- 

 latory beam from our photo- 

 phonic transmitter. The dif- 

 ficulty in ascertaining this will 

 be understood by considering 

 that the sounds emitted by 

 / thin diaphragms and tubes 

 were so feeble that it was im- 

 practicable to produce audible 

 effects from substances in these 

 conditions at any considerable 

 distance away from the trans- 

 mitter ; but it was equally im- 

 possible to judge of the effects 

 produced by our articulate 

 transmitter at a short distance 

 away, because the speaker's 

 voice was directly audible 

 through the air. The extreme- 

 ly loud sounds produced from 

 lampblack have enabled us to 

 demonstrate the feasibility of 

 using this substance in an ar- 

 ticulating photophone in place 

 of the electrical receiver for- 

 merly employed. 



The drawing (Fig. 2) illus- 

 trates the mode in which the ex- 



d 



