182 Transactions of the Horticultural Society. 



27 



obtained : the lower pipe should entei* the boilei- whei'e it has least tend- 

 ency to cool and check the fluid rising to the upper pipe from the fire 

 surface. 



7th, In a close boiler a pipe may, at any distance from the boiler, nse 

 to any height and descend again ; but it must neither rise twice, nor dip, 

 after leaving the boiler ; where it is necessary to raise it, there should be an 

 open pipe inserted at each extremity, of the height of the rise : advantage 

 has been taken of this circumstance to avoid doorways, {Jig. 28.) 



" 8th, A certain quantity of motion would be obtained by a single ho- 

 rizontal pipe between any points except the bottoms of the vessels ; but, 

 the nearer to the surface, the more motion will be obtained j and, with one 

 pipe, there must be a double current in it, 



" 9th, The retarding effect of friction is directly as the length, and in- 

 versely as the diameter, of the pipes j it is also increased by every bend and 

 angle in the pipes. 



" 13. Having considered the circumstances necessary to the motion of 

 the fluid in pipes^ the next enquiry must be the quantity of heat a liquid 

 can convey in a given time j and the quantity of surface required to com- 

 municate it to the air of the housei It is a fact ncrt so generally known as 

 it ought to be, that if we communicate a certain quantity of heat to a 

 liquid^ it will give out exactly the same quantity again in cooling to its for- 

 mer temperature ; less nor more it cannot afford. It is equally true that, 

 with the same temperatures, equal and like surfaces give off equal quanti- 

 ties of heat to air,&c. j and, consequently, the quantities of heat exchanged 

 under given cii'cumstances are measurable quantities, and this subtile ele- 

 ment is brought within the domain of science. 



" 14; I have shown how to estimate the quantity of heat required for a 

 forcing-house, in my book on warming and ventilating (art. 70. and 71.), 

 and have since had to assign the proportions for houses of the largest size, 

 and the most different from the ordinary forms of any in this country j 



