For the first-described model--the simplest--the following materials are needed: some thin whitewood, 1/16 inch thick (as prepared for fret-sawing); some spruce sticks, ¼ inch square (sky-rocket sticks are good); a sheet of heavy glazed paper; a bottle of liquid glue; some of the smallest (in diameter) brass screws, ¼ to ½ inch long; some brass wire, 1/20 inch in diameter; 100 inches of square rubber (elastic) “cord,” such as is used on return-balls, but 1/16 inch square; and a few strips of draughtsman’s tracing cloth. [Illustration: _A_, _B_, blank from which propeller is shaped; _P_, _P_, pencil lines at centre of bend; _C_, _D_, sections of blade at points opposite; _E_, _G_, propeller after twisting; _H_, view of propeller endwise, showing outward twist of tips; also shaft.] As the propeller is the most difficult part to make, it is best to begin with it. The flat blank is cut out of the whitewood, and subjected to the action of steam issuing from the spout of an actively boiling tea-kettle. The steam must be hot; mere vapor will not do the work. When the strip has become pliable, the shaping is done by slowly bending and twisting at the same time--perhaps “coaxing” would be the better word, for it must be done gently and with patience--and the steam must be playing on the wood all the time, first on one side of the strip, then on the other, at the point where the fibres are being bent. The utmost care should be taken to have the two blades bent exactly alike--although, of course, with a contrary twist, the one to the right and the other to the left, on each side of the centre. A lead-pencil line across each blade at exactly the same distance from the centre will serve to fix accurately the centre of the bend. If two blocks are made with slots cut at the angle of 1 inch rise to 2¼ inches base, and nailed to the top of the work bench just far enough apart to allow the tips of the screw to be slid into the slots, the drying in perfect shape will be facilitated. The centre may be held to a true upright by two other blocks, one on each side of the centre. Some strips of whitewood may be so rigid that the steam will not make them sufficiently supple. In this case it may be necessary to dip them bodily into the boiling water, or even to leave them immersed for a few minutes; afterward bending them in the hot steam. But a wetted stick requires longer to dry and set in the screw shape. When the propeller is thoroughly dry and set in proper form, it should be worked into the finished shape with the half-round file, according to the several sections shown beside the elevation for each part of the blade. The two strengthening piece’s are then to be glued on at the centre of the screw, and when thoroughly dry, worked down smoothly to shape. When all is dry and hard it should be smoothed with the finest emery cloth and given a coat of shellac varnish, which, in turn, may be rubbed to a polish with rotten stone and oil.