150 LECTURES TO SCIENCE TEACHERS. 



given to these instruments by Cagniard de la Tour, because it 

 is said to sound under water. I never heard myself, although 

 I have read in the Odyssey, that those charming though dan- 

 gerous young ladies named Setprji/ee did sing under water, but I 

 believe that is the derivation of the word, and I leave it as 

 I find it. Sirens are entirely unknown as musical instru- 

 ments, though they have played an important part, not only in 



FIG. 7. Seebeck's Siren. 



acoustics, but in the investigation of light ; singularly enough 

 they are used for saving life. In going over the Exhibition 

 galleries you will see some enormous steam sirens wherein 

 you can study the arrangements. They are intended to be 

 blown on the coast by means of steam, and to send out to 

 sea a powerful sound warning mariners away from dangerous 

 rocks. The simplest form used in the laboratory is a rotating 



