1872.] Natural and Artificial Flight. 31 
Any pressure applied to the rubber forces the air out of 
the basin into the tube, and if the pressure ceases the air 
re-enters the basin, in consequence of the elasticity of the 
spring. The registering apparatus comprises a_ similar 
basin, to the rubber of which is attached a lever carrying a 
Fic 1. 
tracing-style. The motion imparted to the first basin is 
transmitted, by the air confined in the India-rubber tube, to 
the membrane of the receiving apparatus. In employing 
India-rubber tubing it is necessary to prevent the elongation 
of the tube by its own weight as the bird rises in the air, as 
Fie. 2: 
the elongation would cause a rarefaction of the air in the 
interior of the tube, and consequently interfere with the 
signals recorded. The bird is thrown off at one end of the 
enclosure,, the dovecote in which it is ordinarily kept being 
placed at the opposite end. The bird, in endeavouring to 
