The condenser cell is made as previously mentioned for the focussing tube. The size is regulated by that of the condensing, lenses plano-convex lenses 4 1/8" diameter being used in this lantern, as the same were obtained from an over stocked dealer at a very low price. The usual sizes vary from 4 1/8" to 4 1/2" diameter, the smaller ones being quite as good for this lantern as the larger, and the reader will find it to his advantage to look up the lenses, and see what may be obtainable at less than usual prices. The convex faces of the lens are together with only about 1/8" to 1/4" space between. The tubes are 1 3/4" long, with narrow flanges not over 1/8" wide on the outside. The lenses are kept in position by punching V shaped lugs in three or four places, the points being bent inward after the lenses are in place. The body of the lantern is made of sheet aluminum, about 24 guage, this metal having properties which peculiarly adapt it for that purpose; it radiates heat so rapidly that the hot flame of the burners does not heat it to near the extent it would brass or Russian iron. The sheet size is 6 ft. long, 12" wide, a piece this size 24 guage, weighing about 1 3/4" pounds and sold at about 75 cents per pound. As it cannot well be soldered, joints are made by riveting, the rivets being made from brass escutcheon pins, as previously mentioned, the heads inside. But little of the rivet should project for heading up. The shape of the body is practically that of a box 8" long, 7" high and 7" wide, the top being curved as shown. One strip is used for the sides, top and bottom, a piece 28" long and 8" wide being required, the lap joint being made at one of the lower corners. Ten 1/2" holes are punched in the bottom for admitting air.

The front or condenser end has a 1/2" flange all around fitting inside for riveting, and a hole in the centre about 4 1/4" diameter, to which is riveted a flange 1" wide for holding the condenser cell. This flange, also made of aluminum, has lugs all around the inner edge for riveting to the end. The rear end has a large door with hinge on the right side, made by bending over lugs left on the door, and also the piece cut out for same.

Smaller lugs are left on the left side for bending over to hold a piece of wire with an eye end for fastening. A hole 4" long and 2 wide is cut in the centre of the top. A 2" flange is then fitted to this hole by riveting. A chimney 8" high is fitted to the outside of this flange ; a monitor top is fitted to the chimney. The chimney is not fastened, as it is removed when not in use to reduce the space required for packing away. The body is fastened to the castings F' and F" by four round head machine screws, holes being drilled and tapped for same.

The burner is made as follows: - To the centre of a piece of 1/2" square brass tubing T, Fig. 7, 4" long is soldered three acelylene burners, after drilling 1/4" holes for admitting the gas from tube to burners. The outer end of the tube is then closed by turning down a section of the top or burner side, after cutting away with a hack saw the other three sides. This is done to prevent having a soldered joint of the upper or hotter side. The joint is well sealed with hard solder, and should be a good job to avoid leaking. If the reader does not feel equal to doing this have it done by a plumber, as it will cost but little. The other end is then closed in the same way, making the finished tube 3" long, and a piece of 1/4" brass tube 6" long, fitted thereto by sweating after drilling a hole to admit the end of same. The arms of the burners are at an angle of 45° with the tube.

The burner and reflector holder consists of a piece of 1/2" brass tubing 0, Fig. 8, 3" long fitted to a hole drilled in the top of the casting F" about 1" to the left of the centre. The exact position is found after the burner and holder are completed, the object being to bring burner and reflector exactly in line with the centre of the condenser. A piece of brass rod P 1 1/2 x 3/4" x 5/8" is drilled at one end for the tube 0, and fitted with a set screw p. A 1/4" hole is drilled at the other end for the tube of the burner, and a set screw fitted at that end. The reflector holder R is a piece of brass rod 2" x 3/4" x 5/8" drilled at one end for the tube 0, and fitted with a set screw. At the other end a piece of 1/8" round brass rod is fitted to a vertical hole, and also fits a hole to be found on the back of metal reflectors. One about 4" diameters is a good size. A piece may have to be cut out at the bottom to fit around the burner tube. The burner tube after being put through the holder P is bent downward and carried through a hole in the back end of the body. A 1/4" lever handle air cock is then soldered to the end, and the rubber tubing from the generator pushed well into the end of the cock. This method of fitting burner and reflector enables accurate adjustment to be made, a very important feature as will be learned when using the lantern. A \" hole is cut on either side of the lantern at about the centre, and fitted with pieces of ruby glass, giving a chance to view the flame while using the lantern and without opening the door. The lantern is now complete with the exception of the slide holder, which together with the acetylene generator, slides and coloring of same, will be described in subsequent numbers of this magazine.

Note: - The castings, tubing and other parts necessary to make this lantern will be offered as a premium should a sufficient number of readers make request to have this done.

A comparison of gasoline and alcohol with regard to their relative heating value is possible after recent Austrian experiments. For motive purposes a pair of nominal 8 II. P. engines, one designed for alcohol and the other for gasoline, were compared. The gasoline had a specific gravity of 0.7 and a calorific value of 7,700 calories per litre; the consumption per horse-power was 340 grammes. The denatured alcohol (methylated spirit) was of 90 per cent, strength, and had a calorific value of 4,900 calories per litre ; its consumption was 373.5 grammes per horse power. The efficiencies were, therefore, 10.5 per cent, for the gasoline, and 28 per cent, for the alcohol.