TJie Trials of Light Portable Motors at Plymouth. 589 
Doubtless some practical objection may be raised to the use 
of a tubular boiler like that of Messrs. Simpson for rough 
agricultural purposes. The boiler is no doubt less accessible for 
cleaning than flue boilers with cross tubes. 
Looking, however, to the great disparity of the results, it may 
be questioned whether the supposed power of using very dirty 
water in a flue boiler is not purchased too dearly. A farmer 
might be very well content to take some trouble in getting 
reasonably good feed water if by so doing he secured (1) a 
lighter boiler to drag about, (2) a saving both in cost and cartage 
of nearly half the coal. To adopt a thoroughly bad boiler, merely 
because it is supposed that dirty water may be used in it with 
impunity, is very bad engineering and false policy also. 
Summary of Engine Results 
Simpson, 
Strickland 
& Co., 
Dartmouth 
E. R. & F. 
Turner, 
Ipswich 
Adams <fc Co., 
Northampton 
Piston speed in feet per minute . . . 
298 1 
263 0 
240 3 
5641 
5175 
6-201 
5 042 
3-997 
5003 
0-894 
0 773 
0-807 
Brake-horse-power per cwt. weight of 1 
■3151 
•1095 
•0926 
Cost of engine per brake-horse-power . 
£19 16s. 
£21 18s. 
£22 18s. 
Steam. 
Steam used per indicated horse-power "1 
35-75 
64-73 
57-75 
Coal. 
Per indicated horse-power per hour, lb. 
4 099 
8-461 
9-66 
Per indicated horse-power per hour, if "| 
condensed exhaust steam had been J> 
4-072 
7917 
returned to feed tank as usual . . .J 
4-4 
1-2 
1-6 
These figures show the enormous superiority in economy of 
the small compound engine to the two others. The compound 
engine works with half the expenditure of coal required by the 
single cylinder engines, and, as might be expected, as a conse- 
quence develops three times as much power per cwt. of weight 
of engine and boiler. The compound engine had some advan- 
tage in its higher steam pressure, some advantage in its higher 
piston speed, and some advantage, it is believed, in the drier 
steam supplied from a boiler with a reasonable amount of super- 
heating surface. It has also a distinctly better mechanical 
efficiency, which, however, is partly due to the absence of the 
feed pump and governor, and, so far as it had an increase of 
efficiency in this respect, the gain is not fairly to be credited to 
