REMARKS ON STEAM AND HOT WATER. 
209 
course was plentiful. But the best result which, perhaps, originated 
from this, or some similar trial to introduce steam without heat, was 
the idea of employing these two fluids in combination. Hence has 
arisen the steam forcing system, so efficiently introduced at Sion 
Gardens, and elsewhere, by the late Mr. Tredgold himself. 
From steam to hot water was an easy transition; for though the 
rarer fluid evolved more heat, the heavier was more manageable, 
because less ingenuity and niceness were required in the fabrication of 
the apparatus. Several engineers came forward with specific plans, 
some of which have been secured by patents. Some are on the first 
and simple plan of Atkinson, viz., with a boiler at one end of the house, 
and a cistern of equal capacity at the other, connected by upper and 
lower pipes, as has already been described. Some have open boilers 
with pipes acting on the syphon principle, whereby atmospheric pres¬ 
sure, it is supposed, is added to the weight of the colder water in the 
pipes to accelerate the circulation. Some have close boilers of various 
shapes, with connecting pipes or tubes variously disposed, and of 
different forms ; some of the latter are circular, others square, and some 
are spread out like a table, two feet wide, with raised edges, and move- 
able covers to prevent, or allow, the escape of steam. These last are 
particularly convenient for the purposes of nurserymen in forwarding 
seedlings or cuttings along the fronts of their houses, especially if the 
metal covers have a coat of soft moss laid over, on which the pots are 
placed. Some engineers, in order to obtain a larger radiating surface, 
divide the large tubes into three or four smaller ones, uniting them in 
pannels through which the hot water traverses backward and forward 
in its way back to the boiler. 
Of late there have been considerable improvements, or alterations, 
made in the construction of the boilers. The larger the body of water 
to be heated is, the longer time it requires to be put in motion; but 
when once thoroughly heated, the longer it will continue in motion and 
give out heat. On the other hand, if the boiler be small, and have a 
large surface exposed to the action of the fuel, the water is quickly 
heated, and the circulation almost instantaneous. If a small boiler has 
also a small system of tubes, the effect will be sudden, but transitory ; 
but if a large and complicated system of tubes be attached to a small 
boiler, the circulation will be at first rather languid; and yet when the 
whole is fairly heated and in motion, the large system of tubes will 
continue to evolve heat long after the fire is extinguished. It appears, 
therefore, that a small boiler, with a complicated range of tubes, is 
more economical than a large boiler with only a leading and returning 
pipe. 
VOL. IV.—no. xlviii. u 
