230 



ANIMAL MECHANISM. 



the pectoral muscles, a small instrument is slipped, which is 

 intended to show the dilatation of the muscles, and is constructed 

 in the following 1 manner: 



A little metal pan (fig. 93), containing within it a spiral 

 spring, is closed by a membrane of india-rubber. This closed 

 pan communicates with a tube transmitting air. 



FlO 94 I |>. liim-nl in d. 'termini' liy t'ic electrical nml . 



methods, :it tlio MIIIIC. time, tin- l'iv lUi'lii'V uf til'' movements of the wing 

 and the rvl.itivc duration* uf its c'.evati m and deiires.siuu. 



Madi ]in ^siire on the india-rubber membrane depresses 

 it, and the spring ^ives way; the air is driven out of the pan, 

 and escapes by tin- tube. When the pressure ceases, the air 

 is retiirnrd to the instrument by 1 lie elasticity of the spring 



