Transactions of the Horticultural Societi/. 



181 



Tredgold has formed a table from Dubuat's Prindj^es d'Ht/drauUque, which 

 we do not think it necessary to copy.] 



" 12. From the common principles of hydrostatics, and the equations we 

 have obtained, the following practical deductions may be derived : — 



" 1st, The more expansible the liquid is, by a given change of temper- 

 ature, the greater will be the velocity. 



" 2d, All other things being the same, the velocity will be increased in 

 proportion to the square root of the depth of the boiler; therefore, in a 

 boiler four times as deep, the velocity will be doubled. 



" 3d, If there be sufficient service of pipe for the object required, a re- 

 servoir is not necessary to the motion of the water; a simple bent pipe 

 (^fig. 24'.) being all that is essential to motion ; the reservoir is only to 

 reserve a hot mass of water to maintain the heat after the fire has gone out, 



" 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 corresponding to its velo- 

 city, its capacity need not be further increased, except as a reservoir of 

 heat, to act when the fire ceases to burn. {fig. 25.) 



" 5th, Where heat is required only during the action of the fire, a 

 large surface in proportion to its capacity may be used with advantage, to 

 give off heat over the descending pipe {figs. 26. and 27.): cooling in this 

 manner will increase the velocity. 



" 6th, The aperture of the upper pipe should not be more than about 

 1 in. below the surface of the water, or as much as prevents its drawing 

 air, in an open boiler ; but the lower it is below that, the less effect will be 



N 3 



