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An efficient mode of working an engine with a uniformity of force, by means of a fluid that is constantly diminishing is its elasticity, is, we believe, a problem not yet solved. Another patent for precisely the same object as Mr. Bombas's, was granted on the 1st of June following, to W. Mann, of Effra-road, Brixton, Surrey, who was of course uninformed at the time of his having been anticipated.
Nevertheless Mr. Mann pursued his undertaking, published a pamphlet descriptive of his plans, accompanied by drawings, and endeavoured to raise a company to carry his project into operation. Whether he actually carried it experimentally into practice we are uncertain, but a drawing of the carriage and reservoirs of compressed air are given in the 5th Vol. N. S. of the Register of Arts:-
"Mr. Mann proposes, like his predecessors, to employ a series of strong metallic recipients, similar to the cylindrical vessels used for portable gas, into which thirty or more atmospheres are to be condensed by the power of a steam-engine, water mill, or other adequate prime mover. A sufficient number of these vessels are stowed in a case adapted for the purpose, which is to be fixed underneath the carriage; a tube, communicating with all the recipients, is to convey the compressed air to two working cylinders, having the apparatus common to high pressure steam-engines, the piston rods of which will give motion to a crank on the axis of the hind running wheels. It is proposed to work expansively, and to vary the cutting off the stroke, according to the degree of elasticity of the air.
"The velocity Mr. Mann proposed to travel, was 14 miles in the hour, which he calculates will require 2,000 cubic feet, of the natural density, to propel a carriage weighing, with its load, two tons. When the roads are in a bad state, it is intended to charge the vessels with a greater number of atmospheres, to overcome the increased resistance.
"The patentee states, that the carriage is constructed(?) to carry 75 cubic feet of compressed air, which, at a density of thirty-two atmospheres, is sufficient to propel it 14 miles; and if the air were compressed to be equal to 48 atmospheres, that quantity would propel the carriage 23 miles; and if to 64 atmospheres, 34 miles. The average cost of the power is calculated at one penny per mile; that is, if a steam-engine be employed to effect the compression of the air into the recipients, the cost in coals of such steam power, to condense a volume of air sufficient, by its subsequent expansion, to propel a carriage one mile, is one penny.
“Mr. Mann, however, most know that this would only form one item in the expense of working a carriage. The proposition of propelling by a process of this kind, is certainly specious; but those who have given the subject their best attention, consider that no practical means have yet been devised to compensate for the constantly decreasing expansive force of the air in the recipients."