The result is remarkable, being less than 2 lbs. weight per horse-power, especially when one considers the state of development to which the steam engine had attained at the time these experiments were made. The fining down of the internal combustion engine, which has done so much to solve the problems of power in relation to weight for use with aircraft, had not then been begun, and Maxim had nothing to guide him, so far as work on the part of his predecessors was concerned, save the experimental engines of Stringfellow, which, being constructed on so small a scale in comparison with his own, afforded little guidance. Concerning the factor of power, he says: ‘When first designing this engine, I did not know how much power I might require from it. I thought that in some cases it might be necessary to allow the high-pressure steam to enter the low-pressure cylinder direct, but as this would involve a considerable loss, I constructed a species of injector. This injector may be so adjusted that when the steam in the boiler rises above a certain predetermined point, say 300 lbs., to the square inch, it opens a valve and escapes past the high-pressure cylinder instead of blowing off at the safety valve. In escaping through this valve, a fall of about 200 lbs. pressure per square inch is made to do work on the surrounding steam and drive it forward in the pipe, producing a pressure on the low-pressure piston considerably higher than the back-pressure on the high-pressure piston. In this way a portion of the work which would otherwise be lost is utilised, and it is possible, with an unlimited supply of steam, to cause the engines to develop an enormous amount of power.’ * * * * * With regard to boilers, Maxim writes,-- ‘The first boiler which I made was constructed something on the Herreshof principle, but instead of having one simple pipe in one very long coil, I used a series of very small and light pipes, connected in such a manner that there was a rapid circulation through the whole--the tubes increasing in size and number as the steam was generated. I intended that there should be a pressure of about 100 lbs. more on the feed-water end of the series than on the steam end, and I believed that this difference in pressure would be sufficient to ensure a direct and positive circulation through every tube in the series. The first boiler was exceedingly light, but the workmanship, as far as putting the tubes together was concerned, was very bad, and it was found impossible to so adjust the supply of water as to make dry steam without overheating and destroying the tubes.