Seguin designed his first Gnome rotary as a 34 horse-power engine when run at a speed of 1,300 revolutions per minute. It had five cylinders, and the weight was 3·9 lbs. per horse-power. A seven-cylinder model soon displaced this first engine, and this latter, with a total weight of 165 lbs., gave 61·5 horse-power. The cylinders were machined out of solid nickel chrome-steel ingots, and the machining was carried out so that the cylinder walls were under ⅙ of an inch in thickness. The pistons were cast-iron, fitted each with two rings, and the automatic inlet valve to the cylinder was placed in the crown of the piston. The connecting rods, of ‘H’ section, were of nickel chrome-steel, and the large end of one rod, known as the ‘master-rod’ embraced the crank pin; on the end of this rod six hollow steel pins were carried, and to these the remaining six connecting-rods were attached. The crankshaft of the engine was made of nickel chrome-steel, and was in two parts connected together at the crank pin; these two parts, after the master-rod had been placed in position and the other connecting rods had been attached to it, were firmly secured. The steel crank case was made in five parts, the two central ones holding the cylinders in place, and on one side another of the five castings formed a cam-box, to the outside of which was secured the extension to which the air-screw was attached. On the other side of the crank case another casting carried the thrust-box, and the whole crank case, with its cylinders and gear, was carried on the fixed crank shaft by means of four ball-bearings, one of which also took the axial thrust of the air-screw. For these engines, castor oil is the lubricant usually adopted, and it is pumped to the crankshaft by means of a gear-driven oil pump; from this shaft the other parts of the engine are lubricated by means of centrifugal force, and in actual practice sufficient unburnt oil passes through the cylinders to lubricate the exhaust valve, which partly accounts for the high rate of consumption of lubricating oil. A very simple carburettor of the floatless, single-spray type was used, and the mixture was passed along the hollow crankshaft to the interior of the crank case, thence through the automatic inlet valves in the tops of the pistons to the combustion chambers of the cylinders. Ignition was by means of a high-tension magneto specially geared to give the correct timing, and the working impulses occurred at equal angular intervals of 102·85 degrees. The ignition was timed so that the firing spark occurred when the cylinder was 26 degrees before the position in which the piston was at the outer end of its stroke, and this timing gave a maximum pressure in the cylinder just after the piston had passed this position.