Now draw a diagonal line from D to C, which will give you an angle of about sixty degrees. Now cut a templet or set square out of card or thin wood, corresponding with angle C B D, thus ([Fig. 7]).

Now with line F G on the templet corresponding with line D E in [Fig. 6], draw E F, and continue this until you come to the crown—i.e. the part where the valve is fixed. Now draw diagonal lines, similar to B E, all the way up (as shown in [Fig. 6]), which gives the different sizes of the meshes to be used in forming the net from the equator to the pole; and supposing you have decided to have twelve gores to form your balloon, you would then have forty-eight rows of meshes to go round the balloon, and so on, according to the number of gores of which the balloon is composed.

Now for making the netting from the equator to the hoop, concerning which the following instructions are to be observed. The first set, or row, of meshes below the equator are to be of the same length as those at the equator with one-fourth added—i.e. one-quarter longer; the second set, or row, of meshes from the equator are to be one-quarter longer than the last; the third set from the equator to be one-third longer than the second set; the fourth set one-third longer than the third set; the fifth set, or row, is called the drawing line, and is one-third longer than the last. Then come the cords, or leading lines, which are fastened to the hoop, to which the car is attached. This is the true way to make a proper balloon net, and on the same principles you may make the meshes much larger by setting them out three to the gore instead of four—indeed, they are often made in this manner for economy’s sake—and, instead of having a leading line to each row of meshes, two are frequently blended into one. The material to be used should be the best three-strand Italian hemp netting-line, and you must bear in mind that the meshes at the crown should be very fine, increasing in strength as you go downwards.

The last process in connection with this subject is

THE GAS

with which the balloon is to be inflated. It may be well for you to refer to the chapter by Dr. Scoffern, on the apparatus and method of inflating balloons with hydrogen gas, with his illustration of the apparatus; but as I am going more minutely into details, I give you here the quantities of ingredients for generating sufficient gas to fill a given-sized balloon. Thus, for instance—

Diameter
of
Balloon.		Sulphuric
Acid.		Zinc.Water.Size of
Generator.
24in.24oz.16oz.5pts.4qts.
20„14„10„3„4„
18„10„6„2„5pts.

The zinc and water are put into the generator first and corked down, and connections made with the iron or composite pipe to the purifier, which merely contains water (three parts full), and a small quantity of lime—say, a piece the size of a walnut to a pint of water. Should there be any leakage round the pipe, stop it with loam or clay. Pour the acid into the generator, through the feed-pipe, with a funnel, in small quantities at a time. As the gas passes into the balloon you can tell how quickly it is forming by the bubbling sound which is taking place in the purifier. If you were to pour all the acid into the generator at once, you would burst it. When you hear the bubbling noise diminishing, add more acid.

Now there is another point you must understand—i.e. to be able to find the cubic capacity in feet of a balloon of a given diameter, which is done in the following simple manner:—

Diameter 2 ft. (or 24 in.). Multiply by diameter = 4. Multiply by diameter again, = 8. Now multiply by decimal numbers ·5236 = 4·1888.