88 Professor Alex. B. W. Kennedy [April 21, 



are dealing with a material which is liquid at ordinary temperatures 

 and pressures, so that in its working condition it is a vapour and not 

 a gas, and its temperature cannot be raised without at the same time 

 raising its pressure. Considerations of safety and strength of our 

 materials become here very important, but even if we left them out of 

 account altogether, and raised the value of the maximum working 

 pressure of steam engines from its present limit of 10 atmospheres to 

 20 atmospheres — that is, 100 per cent. — we should have increased the 

 theoretical maximum efficiency only about 10 per cent., a quantity 

 hardly worth considering in such a case. 



No doubt the direction in which to seek for improvement is in 

 that of what is called super-heating the steam, or raising its tempera- 

 ture after it has been formed — converting the vapour into gas without 

 increasing its pressure. Theoretically this can be done to any 

 extent, and I have no doubt that within the next coming years it will 

 be very largely done. It is no new idea, although it is only recently 

 that the use of mineral lubricants in engines has made it thoroughly 

 practicable. The losses between b and c in Fig. 2 are due to many 

 causes, but chiefly to two. The first of these is that the steam is 

 thrown away at too high a pressure — i.e. that it is not expanded 

 sufficiently far in the cylinder. Mechanically this is remediable at 

 once, but only at the cost of making the engine unduly large and 

 costly for its work. This cause of loss is, therefore, likely to 

 remain. The second is one about which there has been much con- 

 troversy both here and abroad, but which, thanks to the work of such 

 men as Willans and Cotterill and Donkin, is now much cleared up. 

 It is simply this — that as the fresh hot steam is always admitted to a 

 cylinder which has just been emptied of steam having a much lower 

 temperature, a cylinder, moreover, which is made of excellently 

 conducting material, a very large proportion of that steam is at 

 once converted into water on entrance, so that for every cubic foot 

 of steam which leaves the boiler and passes along the pipes perhaps 

 only two-thirds, or even half or less, does work in the cylinder as 

 steam ; the rest passes through the engine as water. It is sometimes 

 partially re-evaporated, but never in such fashion or at such time as 

 to be of much real service in doing work. Here truly is a field for 

 economy, and one with very great possibilities. 



I have talked long about steam engines. The subject is tempting, 

 at least tempting to me, and, after all, steam is still the working 

 fluid par excellence. But I must not forget that my subject has 

 many branches, and must look at some of the others. 



The future of gas engines is one which has great possibilities ; we 

 have seen that they represent, in fact, the highest existing theoretical 

 maximum efficiency. Up to a certain point their progress was asto- 

 nishingly rapid ; at present, for a few years, they have more or less 

 stood still, although the number of them has continually multiplied. 

 Just now there are signs that the manufacturers — just possibly it 



