76 LAWRENCE HARGRAVE. 
Four boilers have been made. The one shown in Plate 1 has 
three coils, 1:6 in., 2°6 in. and 3°6 in. respective diameters, 
made of twenty-one feet of copper pipe, ‘25 in. external, and ‘18 
in. internal diameters, weighing thirty-seven ounces. It is now 
known that a coil of equal capacity can be made weighing only 
eight ounces, and still be excessively strong. 
The cylinder of No. 18 is 2 inches diameter, and the stroke 
is 2°52 in. The feed pump ram is ‘266 in. diameter. The piston 
valves are ‘3in. diameter. The 54; in. steel linkwork and brackets 
on the cylinder bottom are too light, and will not stand the rough 
usage required of them. 
The wings are fourteen inches from the fulcrum to the inner 
edge of the paper surface. The paper is twenty-two inches long, 
four inches wide at the inner end, and nine inches wide at the 
tip. The dimensions are the same as in No. 17 with the addition 
of thirty-two and a-half square inches area at the tip of each wing. 
On one occasion this motor evaporated 14:7 cubic inches of 
water with 4:13 cubic inches of spirit in forty seconds. During 
a portion of the time it was working at a speed of one hundred 
and seventy-one double vibrations per minute. The indigram 
shows a nett mean pressure of 95°6 lbs. per square inch, which 
makes the maximum indicated horse power ‘653. Could this 
speed be relied on continuously for a few minutes, the comparison 
between Nos. 17 and 18 would stand thus :— 
No. 17 with 5 oz. of fuel and water indicates -169 H. P. and weighs 34lbs. 
No. 18 ,, 21 oz. a = se °653 Hi. P. a 7}bs. 
That is, roughly, the weight of motor has been doubled and the 
power increased fourfold. 
Comparing the area of wings, the speed of the engines and the 
wing arcs being nearly the same, the extra -48 H.P. is absorbed. 
in driving the sixty-five square inches of extra surface at the tips 
of the wings. The following tabular statement of some of the 
results of No. 18 will be a guide to anyone experimenting with 
engines of this size and quality of workmanship :— 
