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Nors.—The Valve which regulates the expansion is seen in the bottom of the 
Charging Pump. 
principal features still in use in such machines, viz. :—the evapor- 
ator, the compressor, the condenser, and the regulating valve 
‘between the condenser and the evaporator. 
Although his machine was the forerunner of all the compression 
systems of the present dey, Perkins does not seem to have had 
. any, more 
for practical use than Vallance 
had. Dr. Gorrie in 1845, seems to have taken the steps which 
led to the invention of the cold air machine with which the names 
