362 LECTURE XXX. 



enters it; first, by inclosing it in a case of wood, or any other materials that 

 transmit heat slowly; secondly, by surrounding it with steam, of other heated 

 bodies; and thirdly, by suffering neither water, nor any other substance 

 colder than the steam, to enter or touch it during that time. Secondly, in 

 engines that are to be worked wholly or partially by condensation of steam, 

 the steam is to be condensed in vessels distinct from the steam vessels, or cy- 

 linders, although occasionally communicating with them ; these vessels I 

 call condensers; and, whilst the engines are working, these condensers 

 ought at least to be kept as cold as the air in the neighbourhood of the en- 

 gines, by application of water, or other cold bodies. Thirdly, whatever air or 

 other elastic vapour is not condensed by the cold of the condenser, and may 

 impede the working of the engine, is to be drawn out of the steam vessels, or 

 condensers, by means of pumps, wrought by the engines themselves, or 

 otherwise. Fourthly, .1 intend, in many cases, to employ the expansive 

 force of steam to press on the pistons, or whatever may be used instead of 

 them, in the same manner as the pressure of the atmosphere is now employed 

 in common fire engines: in cases where cold water cannot be had in plenty, 

 the engines may be wrought by this force of steam only, by discharging the 

 steam into the open air after it has done its office. Fifthly, where motions 

 round an axis are required, I make the steam vessels in form of hollow 

 rings, or circular channels, with proper inlets and outlets for the steam, 

 mounted on horizontal axles, like the wheels of a water mill; within them 

 are placed a number of valves, that suffer any body to go round the channel 

 in one direction only ; in these steam vessels are placed weights, so fitted to 

 them as entirely to fill up a part or portion of their channels, yet capable 

 of moving freely in them by the means herein after mentioned or specified. 

 When the steam is admitted in these engines, between the weights and the 

 valves, it acts equally on both, so as to raise the weight to one side of the 

 wheel, and, by the reaction of the valves, successively, to give a circular 

 motion to the wheel, the valves opening in the direction in Avhich the 

 weights are pressed, but not in the contrary; as the steam vessel moves 

 round, it is supplied with steam from the boiler, and that which has per- 

 formed its office may either be discharged by means of condensers, or into 

 the open air. Sixthly, I intend, in some cases, to apply a degree of cold, 

 not capable of reducing the steam to water, but of contracting it considera- 

 bly, so that the engines may be worked by the alternate expansion and con- 



