M. Witz goes on with comparative estimates.  For a Corliss engine and boiler, with chimney, etc., complete, and putting these up, he allows L1,280; for a Simplex gas motor and Dowson producer complete, including putting up, he allows L1,290, which he explains to be average actual prices; but these prices do not cover cost of transport, and M. Witz does not go into cost of masonry for buildings, apart from foundations, etc., for the apparatus and machinery.

As to water, the gas motor takes 215 cubic feet per horse power effective.  A condensing steam engine uses five times as much.

The lubricating oil used at Rouen was a mixture of Russian oil at 430 fr. per ton, and Ferry and Heduit F.H. oil at 900 fr.; the average was 650 fr. per ton, or 2.8d. per pound.  Wanner grease, at 6.4d. per pound, was used for the moving parts.  A steam engine requires less oil for the cylinder, but the same quantity for the moving parts.

The attendance on the gas motor is too much for one man, not enough to occupy two; reckon it at 4s. 91/2d. 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 L1,292 = L193.8 = per day. 12 11
Cardiff coal, 2.643 pounds per actual horse
power per hour; 2.643 x 10 x 75 = in 10
hours 1,982 pounds coal at 22s. a ton. 19 51/2
Oil, 3.36 pounds per day at 2.8d. per pound. 0 91/2
Grease, 0.67 pound at 6.4d. 0 41/2
Wages. 4 91/2
---------
L1 18 4

Gas Engine.

s. d. 
Upkeep, interest and sinking fund at 15 per
cent. on L1,292 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 x 10 x 75 = 1611/4 pounds
at 28s. 2 0
Oil, 0.0084 pound per actual horse power per
hour, or 0.0084 x 10 x 75 = 6.28 pounds at
2.8d. 1 51/2
Grease, 0.754 pound per day at 6.4d. 0 5
Electric kindling, on cost. 0 31/2
Wages. 4 91/2
---------
L1 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.