42 REPORT—1874. 
Description of a Trompe or Blowing-Engine for giving a supply of Coal-gus 
under Pressure for Sensitive Flames. By F, Herpert MarsHatt. 
The apparatus consists of a modification of the ordinary Catalan Trompe, 
whereby pressure is imparted to a stream of gas by the velocity of a fall of water 
carrying the gas with it. 
A vertical glass tube, 6 feet long and 3-inch bore, is enlarged in a funnel-shape 
at the top to about 1 inch; into this fits tightly a cork through which pass two 
tubes of about } inch internal diameter, connected, one with the water-main 
and the other with the gas-main, the tubes passing just through the cork on 
the inside. 
The lower end of the large vertical tube passes through an air-tight cork to 
within an inch of the bottom of a 3-pint bottle. 
A siphon with india-rubber connexion and a screw pinch-cock, having a rather 
larger bore than the vertical tube, passes into the same oldie, as far removed from 
the principal tube as possible, and leads to a sink or waste-pipe. 
A third tube of about j-inch bore passes through the cork about 3 inch into the 
bottle: this tube is connected with the sensitive jet, either directly or, better, 
with the intervention of a regulator in which a few inches of benzol take the 
lace of the water usually employed in such apparatus. The regulator should be 
arge, and the tube leading into it rather less than j-inch bore, to obtain greater 
steadiness of flame. 
The working of the apparatus is frequently improved by inserting a loose piece 
of glass tube, about 3 inch long and of such diameter as to remain supported in its 
position, at the point where the long vertical tube begins to expand. The check 
imparted to the stream of water by this contraction seems to assist the formation 
of water-pistons, so to speak, in the principal tube, instead of allowing the water to 
flow down the sides of the tube in a film without carrying gas with it, as some- 
times happens if the supply of water be not sufficient. 
The connexions being made, and all joints air-tight, water and gas are turned 
on from the mains, and the siphon started in action by holding the finger on the 
sensitive jet for a moment. When all air is expelled from the bottle and 
regulator, the gas is lighted, and the flame is adjusted to any desired degree of 
sensitiveness by regulating the supply of water and gas and the outflow from the 
siphon, care being taken to keep 2 or 3 inches of water in the bottle. 
On the Adoption ( for the general purposes of Navigation) of Charts on Gnomonie 
Projection instead of on Mercator’s Projection. By G. J. Morrison. 
I, 
1. The great circle course or shortest distance between any two points on the 
earth’s surface is shown by a straight line on the chart. By means of a ruler, 
therefore, it is easy to find out in one moment the position of the great circle 
track along the whole course from point to point, and thus to see at a glance if 
there be any obstacles in the way, whereas the plotting of a great circle track on a 
Mercator chart involves the expenditure of a great deal of time and trouble. 
2. When it is impossible to adopt the great circle course on account of obstacles 
in the way, it is easy in a few moments to lay down the best practicable course, 
whereas it is very difficult to do so on a Mercator chart. 
3. The measurement of distances on a Mercator chart is somewhat difficult, 
whereas on these maps distances can be measured with a transparent scale or a 
pair of compasses in a few moments. 
4, The relative position of the various points on the earth’s surface is more 
correctly shown on these maps than on those of Mercator. i 
The great circle course appears to be the shortest and natural route, whereas on 
an ordinary chart it appears to be much longer than the Mercator route, and 
seamen get a better idea from these charts of the proper route to follow than they 
do from a Mercator chart. 
