5G THE GARDENER. [Feb. 



stokehole is unavoidable. Before stating the grounds on which we 

 say that a continuous rise in the flow-pipes is a hindrance rather than 

 otherwise to the circulation of the water, let us inquire the reason why 

 circulation takes place under any method of fitting up the apparatus. 

 The primary reason why water circulates or moves in the pipes is in 

 consequence of the minute and separate particles of which it consists 

 being unable to impart heat the one to the other. If the particles of 

 water were capable of transmitting heat to each other in the same way 

 as the particles of which solid bodies are composed are, it would be im- 

 possible, either through the application of heat to the boiler or by any 

 method of fitting up the apparatus, for circulation to take place in the 

 pipes. We would also here observe that in consequence of the inability 

 of the particles of which water consists to communicate heat to one 

 another, every particle of the body of water contained in the appara- 

 tus at the time of lighting the fire must come in contact with the 

 point on which the latter acts, and again in contact with a colder point 

 in the apparatus, before it can contribute to the general warmth of the 

 structure to be heated. The immediate reason, however, why the 

 water circulates in the pipes is because of the inequality of the specific 

 gravity of the particles at different points of the apparatus, the in- 

 equality being caused by the application of heat to a particular point, 

 while the water is being cooled at all the other points. 



Perhaps our young readers will better understand what is here 

 meant if we say that when a fire is lighted in the furnace beneath the 

 boiler, the material of which the latter is made transmits the heat 

 generated by the combustion of the fuel to the particles of the water 

 in direct contact with the inner surface of the metal, thereby raising 

 their temperature, in consequence of which they expand and become of 

 less specific gravity, or lighter in proportion to their size than the colder 

 particles above them. Here the law of gravitation as it applies to 

 liquids comes into operation, and in obedience thereto the heated or 

 lighter particles ascend, their place being instantly occupied by descend- 

 ing colder or heavier particles ; and this ascending of the lighter and 

 descending of the colder particles is what is called circulation of the 

 water, and goes on until the whole body of water contained in the 

 apparatus becomes of the same temperature, — an occurrence not likely 

 to take place so long as the fire is kept burning, unless the boiler 

 power is very much in excess of the work it has to perform. 



We will now endeavour to show why the rise in the flow hinders 

 rather than accelerates the circulation of the water in the pipes. A 

 hot -water apparatus fitted up on correct principles will have its 

 highest point of action occupied by the hottest, and its lowest 

 by the coldest, volume of water contained in the apparatus, the inter- 

 vening points being occupied by volumes gradually descending in the 

 scale of temperature, as they recede from the former towards the latter 

 point. Now, when the flow-pipes gradually ascend from the highest 



