Table I. above shows the dimensions of different parts of these three steam motors, as well as their weights.

The Beaumont engine, worked by compressed air, may be generally said to be similar to that described in a paper read before the Society of Arts on the 16th March, 1881, to which, however, some improvements have been since introduced.

The apparatus for compressing the air was placed in the shed.  The air was compressed to 63 atmospheres by a pump worked by a steam engine, and stored in cylindrical reservoirs of wrought iron without rivets.  A pipe led the air from the reservoirs to the head of the tramway, where the cylinder placed on the motor for storing the air during the journey could be conveniently charged.

The air was compressed by means of four pumps, placed two and two in a water-box, and worked by the direct action of a compound engine, with cylinders, placed in juxtaposition, of 8 in. and 14 in. diameter respectively, with an equal length of stroke of 13 in.

TABLE I.

Krauss.       Wilkinson.        Rowan. 
Diameter of cylinder.........d       5.5 in.       6.5 in.        5.1 in. 
Length of stroke.............l      11.8 in.       9   in.        9.8 in. 
Diameter of wheels...........D      31.5 in.      27.5 in.       29.5 in. 
Pressure at which
boiler is worked...........P     220 lb.       147 lb.         191 lb.
(p(d^{2})l)/(2D).............E   1,210 lb.     1,509 lb.         805 lb. 
Total heating surface........S     105 sq. ft.   105 sq. ft.    64 sq. ft. 
Grate surface................G     2.7 sq. ft.   5.4 sq. ft.   3.1 sq. ft. 
Surface of condenser.........C  274.482 s. ft.    None.      861.120 s. ft. 
Weight in running order
(motor only)...............P’ 15,400 lb.    15,400 lb.       9,020 lb. 
Weight in running order
(total)....................P”       -              -        15,400 lb. 
Contents of water tank.......-  28.24 cub. ft.   13 cub. ft.  4.2 cub. ft. 
Contents of coal bunks.......-  14.12 cub. ft. 12.5 cub. ft.  8.5 cub. ft. 
P’E   12.7 lb.      10.2 lb.        11.2 lb. 
P"E       —              —        19.125 lb. 
P’S    146             147          140
P’G  5,722           2,855        2,889
C/S      2.6             —            13.4
C/G    102               —           275

The air, after being forced through the first pump cylinder, passed successively through the other three, the diameters of which were of proportionately decreasing sizes, viz., 8.2 in., 5 in., 3.5 in., and 2 in., and the air on leaving each cylinder passed on its way to the next cylinder through a coiled pipe immersed in flowing water to remove the heat generated.  This cooling surface amounted to nearly 54 sq. ft.

The cooling of the air was very efficient.  In an experiment made on this question, the temperature of the compressor did not vary to the extent of 9 deg.  F. in charging the reservoir from 40 to 63 atmospheres, occupying an hour and a half, the consumption of water during the time being about 1,400 gallons.