384 Steam Engine. 
Clegg^s and Murray'^ s appear to me entitled to consider- 
ation. 
lOthly. But Mr. Woolf of London, seems to have gone 
farther in improving this machine than any other person, 
since the patent of Boulton and WatU 
He has more accurately than his predecessors, ascer- 
tained the law of the expansion of steam, by a volume for 
each pound per square inch on the safety-valve. Hence, 
He can use his steam at a higher temperature than it is 
used in the common engine of Boulton and Watt^ and 
more under the command of accurate calculation. 
He uses it twice over in separate cylinders ; though it 
seems to me, that there is nothing novel in this part of 
his process. 
He applies heat to the hot steam in the second cylinder: 
using oils, or metalline substances of easy fusibility as 
the mean of communicating and preserving heat to the 
steam : this part of his patent seems to me original ; 
though the same idea was communicated by Chancellor 
Livingston to Dr. Priestley ^ but whether previous or 
subsequent to Woolf patent I cannot now say. 
He has contrived a safety-valve, and a method of mea- 
suring the elastic force of steam, which I have thought 
deserving of being communicated by a plate. 
He has superceded the necessity of such frequent pack- 
ings of the piston, by a contrivance of which I have given 
a general account, referring to the publication where a 
plate of it can be found. 
He has given a substitute for a fly wheel, that in cer* 
tain situations will doubtless be useful ; but I have 
thought it sufficient to refer to the description, 6 Nichols. 
Jour. p. .18. 
He has lately introduced a new principle by making 
the steam press in the first instance on a body of oil, 
which re-acts, as I understand it, against the bottom of 
