MUSICAL SOUNDS. 



175 



obtained much better Dy means of goblets more or less filled with water ; 

 they are struck with a short rod, and emit a sound which can be modified 

 by pouring in a greater or less quantity of water ; if the performer is gifted 

 with a musical ear, he can obtain, by a little arrangement, a perfect Gamut 

 by means of seven glasses which each give a note (fig. 175). A prece of music 

 may be fairly rendered in this manner, for the musical glasses frequently 

 produce a very pure silvery sound. We will complete the elementary 

 principles of acoustics by describing a very curious apparatus invented by 

 M. Tisley, the HARMONOGRAPH. This instrument, which we can easily 

 describe, is a most interesting object of study. The Harmonograph belongs 

 to mechanics in principle, and to the science of acoustics in application. 



Fig. 175. Musical glasses. 



We will first examine the apparatus itself. It is composed of two pendu- 

 lums, A and B (fig. 176), fixed to suspensions. Pendulum B supports a 

 circular plate, P, on which we may place a small sheet of paper, as shown in 

 the illustration. This paper is fixed by means of small brass clips. 

 Pendulum A supports a horizontal bar, at the extremity of which is a glass 

 tube, T, terminating at its lower extremity with a capillary opening ; this 

 tube is filled with aniline ink, and just rests on the sheet of paper; the 

 support and the tube are balanced by a counterpoise on the right. The two 

 pendulums, A and B, are weighted with round pieces of lead, which can be 

 moved at pleasure, so that various oscillations may be obtained. The ratio 

 between the oscillations of the two pendulums may be exactly regulated by 

 means of pendulum A carrying a small additional weight, the height of which 

 may be regulated by means of a screw and a small windlass. If we give to 



