Trials of Tradion-Enrjines at Wolverhampton. 537 
The indicator described is that first invented bj Watt, with a 
flat card reciprocating in front of the pencil, and with the piston 
connected directly by its rod to the pencil at " F^". Since the 
day of Watt the indicator has been improved in construction, 
the flat card has been replaced by a piece of paper partaking of 
the character of that ordinarily employed in metallic memo- 
randum books, which paper is wound round a cylinder caused 
to have a reciprocating- revolution by means of a string and 
spring ; and the pencil, instead of being directly attached to the 
end of the indicator piston-rod, is attached to a lever which 
multiplies the motion of that rod, so that the piston of this 
indicator has but a small stroke. The object of this last im- 
provement is to get rid of the undulations arising from the 
momentum that takes place in the piston of the indicator when 
applied to engines working at high velocities. Formerly with 
Watt's indicator it was difficult to obtain steady diagrams from 
an engine working more than 50 revolutions ; by the use of the 
improved indicator good diagrams can be obtained up to 200 
revolutions, but above this they begin to partake of the undu- 
latory character of the diagrams from the old indicators. 
Entries for Trial. — Originally there were 13 engines entered 
for trial in Class XVII., viz., 4 by Aveling and Porter, 1 of Ashby, 
Jeffery, and Luke, 1 by Tuxford and Sons, 2 by Burrell, 1 by 
Maude and Walker, 1 by Howard, 1 by the Perseverance Iron 
Works (Robey and Co.), and 2 by Ransomes, Sims, and Head. 
These last two entries related, however, in fact, to only one 
engine, but one appearing in two characters, the first with india- 
rubber tyres, and the second with iron tyres. Aveling and 
Porter did not bring their 12-horse engine to the trial yard, 
Messrs. Ashby, Jeffery, and Luke, and Messrs. Maude and Walker 
were not ready, and Messrs. Robey kept their engine at Lincoln. 
Thus the 12 engines were reduced to 8, one of which, however, 
— that of Ransomes, Sims, and Head — counted for two entries, 
making 9 entries. These 9 entries may be divided into 5 
distinct groups : first, the locomotive type of boiler, with iron 
driving and steering wheels. Of this type were Aveling and 
Porter's lO-horse, No. 7001 ; their 6-horse, No. 7002 ; Burrell's 
8-horse, No. 3660 ; and Tuxford's 10-horse, No. 2G77. Second, 
the locomotive type with iron wheels containing india-rubber 
between the outer and inner tyre. Of this only one was exhibited, 
viz. : Aveling and Porter's 6-horse-power, No. 7003. Third, 
the Howard safety boiler, 10-horse-power, No. 1170, mounted 
on ordinary iron driving and steering wheels. Fourth, the 
Thomson vertical pot-boiler, with indiarubber tyres to both 
the driving and steering wheels. Of these two were exhibited, 
viz., Ransomes, Sims, and Head's 8-horse-power, No. 2149, and 
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