CXLII. ; 8. H. BARRACLOUGH. 
2. The number of tests made while varying only one working 
condition, should be as great as possible, rarely less than five being 
of any use, and more being desirable. 
3. Not only each working condition, but also each set of work- 
ing conditions should be systematically varied. 
None of the published series of engine tests completely comply 
with these requirements, more especially with the third of them. 
Even the elaborate series of tests made by Willams are very 
disappointing when examined in this respect, the method of vary- 
: ing the sets of working conditions being irregular and unsystematic. 
‘Neglect of these requirements has led to many altogether unwar- 
ranted deductions being drawn from the results of different engine 
tests, for if three or four points only are available to determine 
the position of a curve, and more particularly if these points are 
close together, almost any variety of curve can be made to fairly 
represent them, and consequently all kinds of cylinder condensa- 
tion formulz can be produced, which although they may approxi- 
mately represent the results obtained from any particular set of 
tests are yet quite erroneous as statements of general principles. 
That such has been the state of things is evidenced by the remark- 
ably varied character of the already proposed condensation formule 
some of the more familiar examples of which are quoted herewith." 
The list is not at all exhaustive, indeed under the circumstances 
there is no object in making it so. 
a C log, r 
ia y 
d N+ 
2: W=CA(T,-T,)t 
Sa aleeiet Pete 
1 These formule are so generally known (with possibly the exception 
of the last) that it is not necessary to give any detailed description of 
them. It should be noted however, that in some cases the formule 
not strictly comparable ; for instance in No. 1, “ y” is the ratio of water 
to dry stream, while in No. 3, “x” is the ratio of water to total steam 
Cotterill—* The Steam Engine,” p. 339; No. 2, Thurston—“ Manual of 
the Steam Engine,” p. 508; No. 3, Ibid., p. 517; No. 4, Industries, Oct. 
1890; No. 5. Proc. Inst. Mech. Engrs., 1889; No. 6, Sib. Journ. Eng» 
June 1896. . 
