in the Conslnict'ion of Sleam-Engincs. 345 



rs^iithout difficulty, arrange and determine the same accord- 

 ing to the nature of the case. 



Lastly. I have to observe, that, to avoid unnecessary- 

 tautologies in speaking of the proportion ih^t ought to 

 subsist between the smaller cylinder or the steam measure 

 and the larger cylinder, or the quantity of steam to be ad- 

 mitted to the working cylinder, where a separate smaller 

 cylinder or steam measure is not adopted, though I have 

 mentioned the regular proportions, as, for example, of a 

 measure or quantity equal to one-fortieth of the working 

 cylinder when steam of forty pounds the square inch is to 

 be employed, or equal to one-thirtielh, or one-twentieth, 

 when steam of thirty or twenty pounds the square inch is 

 to be used ; yet these are not the only proportions that may 

 be u^ed ; for, though it may not be advisable that the pro- 

 portion of the smaller cylinder or steam measure should in 

 any case be made nmch smaller than I have stated, vet, iu 

 making it larger, considerable latitude may be allowed: for 

 example, with steam of forty pounds ihe square inch, a 

 smaller cylinder or measure of one-twentieth, or even larger, 

 or of some intermediate proportion, may be employed in- 

 stead of one of a fortieth of the capacity of the larger or 

 working cylinder ; and so with steam of any other given 

 Strength. And it maybe advisable, that in a number of 

 engines this should be the case, because of the difficulty of 

 preventing some waste of steam or partial condensation 

 which might lessen the rate of working, if not allowed for 

 in the size of the smaller cylinder or steam measure ; or in 

 the quantity of steam admitted dircclly from the boiler into 

 the working cvlinder, where no smaller cvliuder or steam 

 measure is employed : and in every case the engine, when 

 got ready for work, whatever may be the proportion that 

 has been adopted as intended to be worked with, should 

 have its power tried, by altering the load on the valve that 

 ascertains the force of the steam, in order that the strength 

 of steam best adapted for the engine i-nay be ascertained ; 

 for it may turn out to be advantageous that the steam 

 --hould be employed, in particular engines of an elastic 

 force, tornLwhat over or under what was first intended. 



Jn witness whcrtof, he. 



LXV. On 



