■346 
Steam Engine. 
with rounds of hemp or cotton, loosely spun or twisted^ 
ivhich is pressed into a pretty compact form by a ringj^ 
which is worked down by screws distributed round the 
ring and working into the body of the piston ; by which 
means the packing is made to fill the diameter of the cy- 
linder pretty closely, and to prevent,^ while the packing re- 
mains sound, any steam from passing between the piston 
and the cylinder. In the usual method, whenever the pis- 
ton, by continued working, becomes too easy, and so oc- 
casions a waste of steam, it is necessary to take off the top 
of the cylinder, even when fresh hemp or cotton is not 
wanted, merely to get at the screws, which serve to force 
the upper ring nearer to the bottom of the piston, by which 
means the packing is forced outwards against the side of 
the cylinder. This is heavy laborious work, and is there- 
fore generally shunned by the man that attends the engine, 
gs long as the engine can possibly be made to work with^^ 
out taking tjhs trouble ; and in consequence of this ne- 
glect a great and unnecessary waste of steam is occasion- 
ed, and a waste of fuel in proportion. 
Mr, Woolf’s improvement on the piston is such as to 
enable the engine-man to tighten the piston without the 
necessity of taking off the cover of the cylinder, except 
when new packing becomes necessary. He accomplish- 
es this by either of the two following methods ? 
He fastens each of the screws into a small wheel, 
which are all connected with each other by means of a 
central wheel, which works loose upon the piston-rod in 
such a manner, that if one of the small wheels be turned, 
it turns the central wheel, and the latter turns the other 
four. The one that is to be first turned is furnished with 
a projecting square head, which rises up into a recess in 
the cover of the cylinder. This recess is surmounted by 
a cap or bonnet, whidh being easily taken off, and as ea- 
^ly put agaip in its plage, there is little difficulty inscre\>> 
