HFATING HOT-HOUSES BY HOT-WATER 
127 
From the common principles of hydrostatics and the equations 
obtained, the following practical deductions may be derived. 
1st. The more expansible the liquid is, by a given change of tem¬ 
perature, the greater will he the velocity. 
2nd. All other things being the same, the velocity will be in¬ 
creased in proportion to the square root of the depth of the boiler: 
therefore, in a boiler four times as deep, the velocity will he doubled. 
3rd. If there he sufficient service of pipe for the object required, 
a reservoir is not necessary to the motion of the water; a simple 
bent pipe (fig. 15) being all that is essential to motion: the reser¬ 
voir is only to reserve a hot mass of water to maintain the heat after 
the fire has gone out. 
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4th. If a boiler have sufficient surface to receive the effect of the 
fire, and the whole apparatus contains as much water as will convey 
the heat from the fire to the heating surface in the time correspond¬ 
ing to its velocity, its capacity need not be further increased, except 
as a reservoir of heat, to act when the fire ceases to burn. (fig. 16.) 
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5thly. Where heat is required only during the action of the fire, 
a large surface in proportion to its capacity may he used with advan¬ 
tage to give off heat over the descending pipe; (figs. 17 and 18) 
cooling in this manner will increase the velocity. 
