A compressed air motor is an exceedingly simple machine--much simpler than an ordinary steam engine. But the air may also be used in an ordinary steam engine; and in this case it can be much simplified in many details. Very little packing is needed, as there is no nuisance from gland leakage; the friction is therefore very slight. Pistons and glands are packed with soapstone, or other self-lubricating packing; and no oil is required except for bearings, etc. The company will undertake the periodical inspection and overhauling of engines supplied with their power, all which is included in the estimates. The total cost to consumers, with air at an average of 5d. per 1,000 cubic feet, may therefore be fairly taken as follows: Min. Max. Cost of air used £6 14 0½ £18 13 3 Oil. waste, packing, etc. 1 0 0 1 0 0 Interest, depreciation, etc., 12½ per cent. on £10, the cost of engine per indicated horse power 1 5 0 1 5 0 -------- --------- £8 19 0½ £20 18 3 The maximum case would apply only to direct acting engines, such as Tangye pumps, air power hammers, etc., where the air is full on till the end of the stroke, and where there is no expansion. The minimum given is at the average rate of 5d. per 1,000 cubic feet; but as there will be rates below this, according to a sliding scale, we may fairly take it that the lowest charge will fall considerably below £6 per indicated horse power per annum.--_Journal of Gas Lighting_. * * * * * THE BERTHON COLLAPSIBLE CANOE. An endeavor has often been made to construct a canoe that a person can easily carry overland and put into the water without aid, and convert into a sailboat. The system that we now call attention to is very well contrived, very light, easily taken apart, and for some years past has met with much favor. [Illustration: FIG. 1.--BERTHON COLLAPSIBLE CANOE AFLOAT.] Mr. Berthon's canoes are made of impervious oil-skin. Form is given them by two stiff wooden gunwales which are held in position by struts that can be easily put in and taken out. The model shown in the figure is covered with oiled canvas, and is provided with a double paddle and a small sail. Fig. 2 represents it collapsed and being carried overland. [Illustration: FIG. 2.--THE SAME BEING CARRIED OVERLAND.] Mr. Berthon is manufacturing a still simpler style, which is provided with two oars, as in an ordinary canoe. This model, which is much used in England by fishermen and hunters, has for several years past been employed in the French navy, in connection with movable defenses. At present, every torpedo boat carries one or two of these canoes, each composed of two independent halves that may be put into the water separately or be joined together by an iron rod.