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responding on both boilers, act precisely in the same 
manner, whichsoever may be in use. 
When the fire is lighted, these are both shut, and 
remain so till the steam is at its full pressure of Alb. 
to the inch, shown by the guage. At that time the 
Western main is opened, by turning the Cock (D, 
the vents at the end of each tier of pipes being pre- 
hour, it is turned off, and as soon as the steam in the 
boiler has recovered its full pressure, the Eastern cock 
(m) is opened: this fills all the greenhouses down to 
the extreme end: the length of this division is about 
820 feet of houses, furnished with 430 yards of pipe 
more orless. After this has been on for half an hour 
it is shut, and the former opened again, which keeps 
up a heat fully sufficient for every purpose: if the 
weather is not very severe, we do not have the fire 
made till two o'clock in the afternoon, and keep it on 
till nine or ten at night, and no longer. 
Our pipes are all iron, 4 inch bore, flanched and 
screwed together with bolts and nuts: the joints are 
made with iron cement, some upon lead flanches, 
and some upon millboard dipped in white lead: the 
latter way is perhaps the closest and best. They rest 
upon wooden supporters, between which and the 
pipe are small iron rollers, to prevent friction by the 
