1G8 



LECTURES TO SCIENCE TEACHERS. 



cycle of 53 sounds, of which he uses about 40. With all 

 that mass of keys of different kinds, described by differ- 



Fio. 9. Perronet Thompson's Keyboard. 



ent names, quarrils, buttons, and flutals, besides the usual 

 twelve keys, it looks a very difficult instrument to play, and 



