ARTIFICIAL REFRIGERATION AND ICE MAKING. LXIII. 
Compressor are represented as when doing exactly the same work 
and under similar conditions as in the ordinary one, the curves of 
pressure rising to exactly the same height as in the upper figure, 
but the vertical lines representing resistances offered to the pistons 
are only about one-third the height of those in the single compressor. 
This results from the effective areas of the large piston (for the 
down strokes) being only two-thirds, and that of the small one 
(for the up strokes) only one-third of the area respectively of the 
ordinary compressor piston. ‘These resistances are it is seen, dis- 
tributed through the whole of both strokes, instead of being con- 
centrated at the upper end of one only. The two right hand 
figures show these diagrams placed around a circle, the left hand 
half of which, or semi-circle, represents an up stroke, and the 
right hand one a down stroke respectively, the letters of reference 
serving asa guide. The distribution of the work performed by 
the compressor pistons during one revolution of the crank shaft 
is thus graphically displayed by the length of the radial lines. The 
upper of the two showing that a relatively large expenditure of 
power is required during about only one-sixth part of a revolution 
in an ordinary machine, while the Antarctic Compressor requires 
& comparative even expenditure of power (amounting to only 
about one-third of the former) but distributed throughout the 
whole of the circle of the crank pins travel. 
Discussion. 
Mr. CruicksHanxk said it was a matter for congratulation that 
the present development of refrigeration was largely due to 
Australian energy and enterprise, and Mr. Selfe had done his fair 
Share of the work. What the author had attempted to do was 
very important, and although it might not be altogether original 
he had done it in a very practical way. He could not do better 
Perhaps than compare the working of refrigerating machinery 
with what takes place in a steam engine. Of course the action 
ofa refrigerating compressor was simply that of an engine reversed. 
The strains in a steam engine are very great, and we endeavour 
