THE STEAM-ENGINE. 123 



into hardly any of the schemes devised for this purpose, "but as 

 you know, for some reason or another, it has "been found not 

 desirable up to the present time at least (for I am sure I should 

 be sorry to limit invention) to employ engines of that kind. 

 At least so far as I know there is not one in practical work ; 

 although there have been some extremely ingenious sug- 

 gestions. The Earl of Dundonald (Lord Cochrane) made a 

 celebrated rotary engine at the place where I was apprenticed. 

 It worked either with air or with steam, and so long as we 

 worked it by exhausting air and letting the atmosphere press 

 upon it, it ran satisfactorily, but when we put steam into it, 

 and it had to support the variations caused by expansion, 

 there were always difficulties. Nevertheless Lord Cochrane 

 was a bold man, and went on. We made a locomotive for 

 the Greenwich Eailway, he would design his own boiler, and 

 that boiler never raised steam to speak of ; and the only result 

 of the steam that was raised was, I am sorry to say, the de- 

 struction of the engine. Earl Dundonald, good sailor as he 

 was, had forgotten his anchorage, he had only anchored his 

 engine by the steam pipe, and when the steam was put on, 

 the engine preferred to twist the steam pipe round instead of 

 causing the driving wheels to revolve, and the unfortunate 

 locomotive was consigned to the scrap heap. There is at the 

 present time under trial a rotary engine of the most extraordi- 

 narily simple character. It is the invention of a Scotchman 

 long resident in America, Mr. Dudgeon, who may be well 

 known to many of you as the inventor of the "tube expander." 

 This engine consists of nothing at all but two spur wheels with 

 teeth that work steam tight in each other, and at their ends 

 work steam tight also against two plates. Assuming the spur 

 wheels to be on horizontal axes placed side by side, and that 

 it is intended they should revolve so that the teeth which are 

 in contact move upwards, then the steam would be intro- 

 duced through one of the end plates a little above the line of 

 centres ; it would there be received into the cavity between 

 two pairs of teeth, and it would press upon the under teeth 

 to drive them down, while it would press upon the upper 

 teeth to drive them up. It might be thought that under these 

 circumstances no motion would ensue ; but- it will be seen 

 that the area of the upper surfaces would be larger than the 

 area of the lower, and thus there would be a preponderat- 

 ing upward effect. After the teeth have passed a particular 



