In constructing a small dirigible balloon, the first and most essential thing is to make a perfect envelope, which can only be had after careful labor. Cotton may be used, but silk makes by far the better gas bag. It is three or four times as strong as cotton, and will last indefinitely with proper care.

The silk must first be cut in lengths of from twenty to thirty yards, according to the size it is desired to make the envelope. Next the silk must be given a thorough bath, in either linseed or spar oil, and hung up by one end to dry. so that the oil will run to the bottom and dry evenly. The drying process depends on the climatic conditions, and I have had it take from one week to five months for my silk to dry. The silk must be thoroughly dry before cutting and sewing.

After the silk has been prepared, the next step is to make a pattern for a single gore of the gas bag, or for a half or at least a quarter of such a gore.

In drafting and cutting the pattern, great care should be taken to see that it is absolutely correct in outline, as if there is the slightest irregularity the silk will draw and tear. The edge of each gore should be cut on a curve which is laid out in the following manner upon a paper pattern: A strip of paper of the same dimensions as a length of the silk is fastened horizontally on a wall. A string is then suspended from two tacks placed at each end of the strip, midway of its width, and allowed to sag until it touches the bottom of the strip. The line thus formed will he the desired curve. The only point to remember is that the gores must be of the proper width to give the desired circumference at the center and that there must be enough margin left to allow for overlapping the seams. Once the pattern is obtained the cutting is easily accomplished.

I have found the most economical and reliable one-man airship to be one made to the dimensions of my "California Arrow," the length of which is three times the diameter, while three and a half times would still be a good proportion. The seams should all be double stitched. The strips are first sewed together with a plain seam about 1/2 inch from the edge. The raw edges are then turned under about 1/8 inch, and sewed down by a second line of stitching 1/4 inch from the first line, thus forming a lap seam. The sewing should be done with good silk.

About two feet from the bottom center of the envelope, make a large neck, or manhole, so the bag can be turned wrong side out and varnished. Directly above this manhole, in the top, a 14-inch valve may be fitted. Although the valve is merely a matter of personal desire, I do not advise building an airship without one. Should the valve be inserted, there must be a cord coming down to the manhole, so that it can be used if needed. About four feet back of the manhole, put in a small neck about six inches in diameter, for filling the bag with gas.

Now the bag being sewed and ready for the coating of varnish, take a six-inch brush and after the envelope has been blown full of air, so that it will hold its shape, commence at one end and paint one or two gores the entire length of the bag. When these have been very carefully done, take the next two gores, and so on until the entire envelope has had the second coating. After this is absolutely dry, turn inside out and do the same thing over. These coats of varnish must be put on until the envelope is air tight, and there is no leakage. Be careful to watch the envelope when filled with air, as the change in temperature will cause the air to expand and is liable to burst the bag, but after watching it a day or two, the hours for expansion and contraction will soon be learned.

This envelope should be entirely incased in a linen square mesh netting, and never a diamond shape, as there will be no end of give with the diamond mesh, and it will be difficult to control the airship when in the air. The squares should be about six inches, and for a ship the size of the "California Arrow" there should be about sixty suspension cords of alternately 6 and 8 feet in length, placed some two and a half feet apart and extending the entire length of the frame. There will be two cords on each point of the finished netting, one for the top and one for the bottom of the frame.

The frame, which is about 45 feet long, should be built of 1 1/2-inch Oregon spruce. It is in the form of an equilateral triangle, and it should be braced every three feet with a 1 1/2 x 1/2-inch strip, the panels thus formed being braced diagonally with piano wire.

The frame should hang about six feet from the bottom of the envelope and should be perfectly adjusted, so that an equal strain will come on each suspension cord.

The propeller should be a two-bladed one, ten feet in diameter, with the pitch about equal to the diameter, and a blade width of 18 inches at the tip. It should be geared to make about 175 revolutions per minute, which is a peripheral speed of the blades of 5,498 feet per minute. The longer the blade and the slower the speed, the more efficient is the propeller within certain limits. The propeller shaft should be made of 16-gage, 1 1/4 -inch seamless steel tubing. The rudder should contain a surface of 36 square feet.

A 7-horse-power air-cooled motor of about 50 pounds weight is sufficient power for this size airship, as the full power of a larger engine cannot be used, and for the novice a 7-horse-power engine is quite sufficient. The motor should be placed about one-third of the distance from the front of the framework and suitably geared to the propeller. A clutch can be fitted if desired, but this is not absolutely necessary. The engine should be carefully watched at all times, as the success of an airship depends upon the motor. The engine should be rigidly inspected each time before going in the air, and special attention should be given to its lubrication, which must be very thorough.

During 1907 I made ninety-two starts, returning to the exact starting point ninety-one times. On the one trip from which I did not return under my own power, the wind came up stronger than the thrust of the propeller, and therefore I was helpless, but my valve gave me the means of a safe descent. Never go into the air when the wind has more power than you have, and you will have little or no trouble. An eight-mile-an-hour wind is a safe limit, although an experienced operator can operate in a wind of from twelve to fifteen miles an hour. Accidents are not necessary if the operator is sure that everything is in working order before he makes an ascension, for when you are once in the air, and things go wrong, it is then too late to remedy them and you will have to take the consequences.

Following are the dimensions of the "California Arrow," which may be used as a pattern: Length, 52 feet; diameter, 17 feet, with a capacity of 9,000 cubic feet. Made of the best Japanese silk, coated with linseed oil varnish. Irish linen netting. Frame, equilateral triangle, 45 feet long by 3 x 3 feet wide, and equipped with a Curtiss 7-horse-power motor of 50 pounds weight. Two-blade screw propeller, 10 feet in diameter and 10-foot pitch, with 18-inch width of blade at tip; peripheral speed, about 5,000 feet per minute. Shaft connected with a countershaft, but no clutch is used. The speed is controlled by a rod eight feet long extending forward from operator to motor and connected to the throttle. The rudder contains 36 square feet of surface. The tiller rope is continuous and passes around a pulley in front of the operator. The rudder can thus easily be controlled by one hand. One thousand cubic feet of gas will lift 65 pounds. The formula for making the gas is 1,000 pounds of sulphuric acid, 1.000 pounds of iron. 5,000 pounds of water, which should generate 3,500 cubic feet of gas.

After the frame and engine and all connections are finished, the airship is ready for its first flight. The airship, of course, is supposedly under cover and protected from bad weather while waiting for the start. The very last thing to do before leaving the aerodrome is to ballast the airship. Mount the frame and arrange things so that the center of balance is about 5 feet back of the motor. Add or take from the ballast until there is about three pounds of ascensive power, and then you are ready for a flight. This should be done about fifteen or twenty minutes before the time of ascension, so that, there will be no delay whatever when the minute arrives. After stepping from the frame and having the ship anchored, walk around and look carefully over everything. The manhole and inflating neck should be made into a safety valve, by taking up several inches and twisting an elastic band around several times, so that in case high altitude or heat from the sun's rays causes expansion, the bands will blow off and give warning before the envelope will rip.

A large open field is preferable for the trial flight. Two saw horses about 4 1/2 feet high will be needed to set the airship on, before the flight, so that when starting the engine the propeller will not strike the ground. Now the airship, we will say, is in the field and you are on the frame with the engine working all right. The rudder ropes are free, and everything all ready. You should have a drag rope of 100 feet attached to the frame about one-third from the back end. This should be carefully laid on the ground free from everything, so that when you rise it will not become entangled. You take your seat slightly back of the center of balance, with the engine running, and when you give the signal, the saw horses are knocked out from under the frame, and you ascend at an angle of about 10 degrees by stepping back a foot or two upon the frame which you are straddling. You now must use your own judgment about your flight, as to how long it will be and where you will try to go, but be careful not to turn your rudder too quickly. This should be operated by two tiller ropes, one in each hand. Move slightly forward for descent, and backward for ascent. The spark and throttle control rods run back along the frame, and can be operated at all points where you stand. In coming down stop the motor about 25 or 30 feet from the ground, and have some one to catch the frame and save the propeller from striking the ground. With proper judgment the airship should come back to the exact starting point, even as close as one or two feet. After the flight is ended, take the airship back to the aerodrome, guv it down carefully, shut off the gasoline, disconnect the spark, and watch the gas bag for expansion. With proper care the airship should stay in that condition indefinitely, and be ready for another flight when you so desire.