46 NOTES ON STATIONARY ENGINES. 



The foaming referred to by Mr. Harvey gives an interest- 

 ing illustration of the principle of convection referred to at 

 the last meeting. 



The perforations in the anti-priming pipe may ho in any 

 convenient position, perhaps rather better on tlio top ; but in 

 this case the pipe should be set down from the top of the 

 boiler a little way, to avoid grof)ving the; shell by the cur- 

 rents of steam, flying past. 



There need bo little fear of trouble with, a parallel motion, 

 the total frictional resistances ai-e smaller than those apper- 

 taining to slides; and so far from small surfaces (per se) 

 giving most trouble, there is no joint in an engine which 

 does as much work and with so little trouble as the " little 

 end," to use a locomotive engineer's expression. One point in 

 tlie parallel motion was not referred to, this is the varying 

 character of the strains when a parallel motion is used for 

 guiding and also for working pump. 



Mr. Ncwall further explained the principle laid down as 

 to the use of the cut-off principle. A variable cut-oft may 

 be in an extreme case adopted, and yet not save as much 

 coal as was consumed in its construction. 



The instances given by Mr. Morgan where long strokes 

 are perfcrable, viz., to winding engines, are quite in order 

 and most interesting ; but tliis preference does not affect 

 their acknowledged disadvantages in connection with constant 

 and unremitting steady driving. The writer was at one 



