572 



THE GARDENER. 



[Dec. 



Here, then, we see that there is a clear turn of the balance in favour 

 of the descending water, and therefore, under the conditions proposed, 

 there will be a circulation, in spite of the dips at g and I. But now, 

 if we suppose the boiler raised to the level of c, we shall have no b pipe 

 at all, but only the height of the boiler 2 feet, while m will be 10 feet 

 instead of 4 : the result will be that the weight of the ascending 

 water would be 20.73646, which would be more than the weight of the 

 descending water, and consequently there would be no circulation. It 

 would, indeed, commence, but by the time the heated water reached/, 

 an equilibrium would be established, and there would be no motive 

 power to force it in either direction. If, again, the boiler were sup- 

 posed to remain, as shown on the diagram, but without any rise at d, 

 then the height of k would be only 9 feet, and yet the water would 

 still circulate, if the temperatures were as stated in the last table ; but 

 if the range of pipes were shortened so as to make the temperature of 

 the water at k 140° instead of 104°, the circulation would cease, for 

 calculation would then show that the water intended to ascend would 

 weigh 14.74194, while that intended to descend would be only 

 14.72001. In short, if in any arrangement we obtain the tempera- 

 tures and the heights of the several ascents and descents, we can 

 calculate to a certainty whether the water will circulate or not. 



A few words may now, in conclusion, be said on some questions that 

 have been raised in the controversy. 



1st. Water is an exceedingly bad conductor of heat ; but this must 

 be understood of it strictly when not in motion. When at liberty to 

 move, its particles become, by what is called convection — i.e., by suc- 

 cessive contact — capable of very rapidly transmitting heat. 



2d. The rapidity of circulation cannot be reduced to any useful rule, 

 because it is so greatly affected by friction, and still more by alteration 

 of direction, in bends of the pipes. 



3d. Water in a pipe that leaves the boiler perpendicularly cannot 

 have any back currents, but if the pipe leaves the boiler horizontally, 



