(71.) The first experiment in which Watt attempted to [Pg125] realise, on a small scale, his conceptions, was made in the following manner. The cylinder of the engine was represented by a brass syringe A B (_fig._ 20.) an inch and a third in diameter, and ten inches in length, to which a top and a bottom of tin plate was fitted. Steam was conveyed by a pipe, S, from a small boiler into the lower end of this syringe, a communication being made with the upper end of the syringe by a branch pipe D. For the greater convenience of the experiment, it was found desirable to invert the position of the cylinder, so that the steam should press the piston P upwards instead of downwards. The piston-rod R therefore was presented downwards. An eduction pipe E was also inserted in the top of the cylinder, which was carried to the condenser. The piston-rod was made hollow, or rather a hole was drilled longitudinally through it, and a valve was fitted at its lower end, to carry off the water produced by the steam, which [Pg126] would be condensed in the cylinder in the commencement of the process. The condenser used in this experiment operated without injection, the steam being condensed by the contact of cold surfaces. It consisted of two thin pipes F, G of tin, ten or twelve inches in length, and the sixth of an inch in diameter, standing beside each other perpendicularly, and communicating at the top with the eduction pipe, which was provided with a valve opening upwards. At the bottom these two pipes communicated with another tube I of about an inch in diameter, by a horizontal pipe, having in it a valve, M, opening towards I, fitted with a piston K, which served the office of the air-pump, being worked by the hand. This piston, K, had valves in it opening upwards. These condensing pipes and air-pump were immersed in a small cistern, filled with cold water. The steam was conveyed by the steam-pipe S to the bottom of the cylinder, a communication between the top and bottom of the cylinder being occasionally opened by a cock, C, placed in the branch pipe. The eduction pipe leading to the condenser also had a cock, L, by which the communication between the top of the cylinder and the condenser might be opened and closed at pleasure. In the commencement of the operation, the cock N admitting steam from the boiler, and the cock L opening a communication between the cylinder and the condenser, and the cock C opening a communication between the top and bottom of the cylinder, being all open, steam rushed from the boiler, passing through all the pipes, and filling the cylinder. A current of mixed air and steam was thus produced through the eduction pipe E, through the condensing pipes F and G, and through the air-pump I, which issued from the valve H in the eduction pipe, and from the valve in the air-pump piston, all of which opened upwards. The steam also in the cylinder passed through the hole drilled in the piston-rod, and escaped, mixed with air,