674 
Report on the Trials of Portable 
in itself, constitutes a complete and valuable reply to the enquiry 
proposed by the Royal Agricultural Society for solution : — 
Maker. 
Lbs. Coal per Brake- 
Horse-power per hoar. 
Difference. 
Percentage of advantapo 
in favour of compound 
Simple. 
Compound. 
system. 
Davey, Paxmau & Co. . . 
2-6 
1-85 
•75 
28 '9 per cent. 
2-7G 
1-94 
•82 
29 ■ 7 per cent. 
2-G8 
2-18 
•50 
18 '6 per cent. 
There is no doubt that McLaren's percentage of advantage 
would have been higher but for the fact (alluded to in the 
account of his trial) that his compound engine worked under 
unfavourable conditions. 
It may be concluded that the introduction of compounding 
into portable engine practice would be followed by a saving of 
more than 25 per cent, in coal, comparison being made between 
engines of both types fitted with automatic expansion gear, 
while there can be no doubt that compound engines, without 
expansive gear of any kind, will surpass the above percentage 
of economy, comparison being made with existing portable 
engines, also without expansion gear. 
With regard to the question of relative weight, involving the 
question of price, the following table gives the weights of the 
six engines already mentioned, viz. : — 
Maker. 
Weiglit ill Tons. 
Simple. 
Compound. 
Davey, Paxman & Co. 
4-91 
5-24 
Foden (traction) . . 
10-42 
11-20 
5-04 
5-46 
The Compound engine weighs, at present, more than the 
simple engine, although requiring a boiler of considerably less 
steaming capacity. After further experience has given makers 
more confidence in the economy to be obtained from com- 
pounding, they may, perhaps, venture on pinching the dimen- 
sions of their boilers a little, and in this way compensate for 
the extra weight of a second cylinder and second valve chest. 
It is quite to the point to remark here that all the Compound- 
