484 Proceedings of the Royal Society of Edinburgh. [Sess. 
the expansion is made by releasing the lever T, when the rubber valve 
springs from its seat and has considerable velocity before the air begins 
to escape, thus ensuring a quick and full opening of the outlet. 
Another method of release was also tried. As has been already stated. 
the ideal form of expansion is the quickest that can be accomplished, but 
the final part of the expansion is the more important, a slight slowing 
of the initial part not being likely to have any bad effect. Accordingly, 
the apparatus shown in fig. 5 was made to meet these conditions. As 
before, the tube Y is connected at C' with the expansion chamber B, fig. 2, 
and at C" with the compressor. The release valve in this case consists of 
a plunger W, which is very accurately ground into the end of the pipe Y. 
This plunger, though fitting quite easily, is air-tight with the aid of a little 
glycerine or oil. U is a catch for preventing the plunger from being 
blown out by the pressure of the air. The action of this release valve is as 
