174 LAWRENCE HARGRAVE. 
pressure, and 1-8 per second with seventy-five pounds. At a 
speed of 2:46 per second the pen marks are illegible, this is when 
using the indicator delineated in last year’s Proceedings. ~*~ 
A thrust diagram shows that— 
2:2 double vibrations per second produce a thrust of ‘75 ibs. 
bL 
2°3 ” ” ” ‘9 ” 
2°44 D0 ” ” 11 ” 
2°5 ” ” ” 1°25,, 
It is noteworthy that a slight increase of engine speed makes a 
large increase of thrust. 
The total weight of the apparatus is 64:5 ounces which includes 
12? ounces for the strut and body-plane and five ounces for spirit 
and water; and by putting on the indicator, Plate x11., it is found 
that ‘169 H.P. is developed when 2°35 double vibrations are made 
_ per second. Plate x1. With 2:5 double vibrations per second 
there would be a corresponding increase of work done. It is in- 
convenient to attach the indicator cord to the cross head. Fasten- 
ing it to the wing arm moving in an arc of 112° must produce a 
slight distortion of the indigram near the ends of the stroke. 
If we load the machine with ten ounces more spirit and water 
to bring it to the same weight as No. 12, which flew three hundred 
and forty-three feet* with thirty-eight double vibrations, it will 
be seen that five hundred and forty-six double vibrations can be 
made by No. 17 which will give a possible range of one thousand 
six hundred and forty yards. 
On starting, the boiler is empty, and warmed up by a Bunsen 
burner : then the spirit holder is heated till the flame ignites, it 
is kept alight by a few shreds of asbestos put into the coil. When 
the flame is fairly underway, part of the boiler gets red hot in a 
few seconds.. Then the wings are.moved up and down a few times 
by hand squirting about a teaspoonful of water into the boiler and 
* The best flights of Nos. 12 and 16 were each three hundred and forty- 
three feet. 
