4 Scientifie Proceedings, Royal Dublin Society. 
each carriage. One end of this sack is attached to the frame of 
the carriage, and the other, which is attached to a rod in connee- 
tion with the brake gear, is free to move. Whenever the air is 
exhausted by the steam jet from the sacks, the free ends collapse, 
and put the brake on. This brake is extremely simple. It is 
not automatic, but, if necessary, could probably be made so. 
There is also the Saunders Air Brake, and Barker's Hydraulic 
Brake, which are used. All these brakes will stop a train run- 
ning at from 40 to 50 miles an hour in from 17 to 23 seconds, 
and in about 250 yards, or less, that is,in a fourth of the dis- 
tance that a train running at the same speed would be stopped 
by the ordinary hand brakes. 
Another means of transmitting power is by electric conductors. 
A four horse-power engine will produce light in this way equal 
to 1,000 candles ; 100 horse-power will equal 25,000 candles, or 
1,250 Argand burners, equal to 25,000 cubic feet of gas per hour, 
equal, at 4s. 6d., to £5 12s. 6d. 
Norre.—The latest experience shows that when the photometer is 
placed in the same horizontal plane as the regulator at a distance of 
16-4 ft., a light equal to 2,400 candles is given. If the photometer is 
lowered 16:4 ft., the same horizontal distance being kept, the photometer 
indicates 8,400 candles. If they are on the same level, the distance 
being 16-4 ft., and the lower carbon placed a little in advance of the 
upper so as not to be immediately below it, the photometer indicates 
6,400 candles. In each case the power necessary to drive the machme 
being 24 horse-power. The cost of working four Gramme machines, | 
allowing 12 per cent. for interest and depreciation, is about 5s. an hour. 
