The attendance on the gas motor is too much for one man, not enough to occupy two; reckon it at 4s. 9½d. a day. These elements enable us to calculate the daily cost of the gas motor, of 75 actual horse power, in comparison with a steam engine of the same size. _Steam Engine_. s. d. Upkeep, interest and sinking fund at 15 per cent, on £1,292 = £193.8 = per day. 12 11 Cardiff coal, 2.643 pounds per actual horse power per hour; 2.643 × 10 × 75 = in 10 hours 1,982 pounds coal at 22s. a ton. 19 5½ Oil, 3.36 pounds per day at 2.8d. per pound. 0 9½ Grease, 0.67 pound at 6.4d. 0 4½ Wages. 4 9½ --------- £1 18 4 _Gas Engine_. s. d. Upkeep, interest and sinking fund at 15 per cent. on £1,292 is, per day. 12 11 Anthracite, 1.156 pound per actual horse power per hour = for 750 horse-hours, at 25s. 6d. 9 10 Coke, 0.215 pound × 10 × 75 = 161¼ pounds at 28s. 2 0 Oil, 0.0084 pound per actual horse power per hour, or 0.0084 × 10 × 75 = 6.28 pounds at 2.8d. 1 5½ Grease, 0.754 pound per day at 6.4d. 0 5 Electric kindling, on cost. 0 3½ Wages. 4 9½ --------- £1 11 8 The big gas engine making its own poor gas, and running 10 hours a day, has thus the best of it in the comparison with the steam engine of equal power. * * * * * A PROJECTING APPARATUS FOR BALANCES OF PRECISION. The luminous projection apparatus illustrated herewith, when adapted to a balance of precision, permits of effecting weighings very rapidly. For the same approximation, the velocity of oscillation becomes five or six times greater, and, by the method employed, the last centigrammes and the milligrammes and their fractions are estimated directly, with immediate verification. As the apparatus is independent of the parts of the balance, it can be placed on all the existing laboratory balances of precision. [Illustration: PROJECTING APPARATUS FOR BALANCES OF PRECISION.] The modification introduced into the balance consists in the displacing of the center of gravity of the beam in such a way as to diminish the sensitiveness, and consequently to obtain a much greater velocity, and then, by optical means, to considerably increase the amplitude of the oscillations.