266 



SCIENCE PROGRESS 



depend upon the compression and expansion of an elastic 

 cushion. The clearance spaces at the tops of the combustion 

 chambers may therefore be reduced to the very small volume 

 needed to bring easily to rest that portion only of the column 

 which rises in the chamber, the main body of the column 

 being brought to rest by the compression of the new charge. 

 Again, for a given height of lift the compression pressure 

 attained is higher in the double-barrel pump, because the 

 returning column gains speed while exhausting the last part 

 of the burnt products and has thus obtained a store of kinetic 

 energy before starting the compression stroke proper. 



Fig. 3. 



A two-cycle pump has been invented by Mr. Humphrey in 

 which there is only one combustion chamber. The diagram 

 of the top of this pump is shown in fig. 3, where a is the 

 admission valve at the top of a tall but narrow part of the 

 chamber b in which the full charge volume extends down to 

 the level oi c c. A number of exhaust valves e lead to a 

 common exhaust outlet o, which may be fitted with a non- 

 return valve or each exhaust valve may carry a light non- 

 return valve on its spindle as shown. The level at which 

 expansion reaches atmospheric pressure is, say, //; this 

 level having been reached by the water, its further movement 

 may either draw in pure air followed by combustible mixture 



