124 LECTURES TO SCIENCE TEACHERS. 



point they act as a slide valve and cut off the steam, and the 

 steam contained between two teeth goes on expanding until 

 a further point is reached where by their divergence thev 

 allow it to escape. I have seen the engine at work, and most 

 certainly 60 Ibs. of steam went into the engine and the ex- 

 haust steam came out perfectly inert. My notion was, that 

 the 60 Ibs. steam was being utilised. I have endeavoured to 

 get results from trials by the dynamometer, but those trials 

 were inconclusive. I merely bring this engine before you as 

 one of the ingenious attempts what its future may be I 

 know not to obtain that which we all feel ought to be 

 obtained, the production of rotary motion from steam at first 

 hand instead of the obtaining it at second hand through 

 reciprocating motion. I may say that this science collection 

 offers very little inducement indeed for me to speak to you 

 about rotary engines, for so far as I know it contains 

 but three specimens. Here, in one by the late Patrick Bell, 

 we have a cylinder bent into a semi-ring, with a con- 

 tinuous slot on its inner side ; a disc, working steam-tight in 

 this slot, carries pistons which you will see are intended to 

 enter and to leave the cylinder edgeways, but while in the 

 cylinder to lie flatways, so as to be pressed upon by the 

 steam. I do not know that this engine was ever more than an 

 idea. I do not know the date of it, and I do not think any of 

 us will look at it as likely to give economical results. Here is 

 another machine which has been commonly classed as a rotary 

 engine, but I am not sure that it is correctly .so classed ; it is 

 the celebrated Disc engine, from which so much was expected 

 at one time. It is in truth a reciprocating engine because the 

 disc reciprocates from side to side, changing the point of 

 contact, and by means of a rod standing out at one of its faces 

 gives rotary motion to the crank. After all there is a crank. 

 The crank is a necessity, and therefore such engines can 

 hardly be classed among the rotaries. The third model I 

 hava here is little more than a Barker's mill. 



There is no doubt that many of the persons who set them- 

 selves to devise rotary engines, do so, because they are under 

 the impression that there is an absolute loss of power by the 

 use of the crank. I need not tell gentlemen who are here 

 to-day, science teachers, that there is no loss of power at all 

 theoretically speaking. As a matter of fact you may by the 

 friction of the shafting and its bearings, by the necessity of 



