Transactions of the London Horticultural Society. 425 



" This remark applies not merely to the earlier apparatus, where the power 

 was inadequate to the work required, but even to the best-constructed 

 modern ones ; and the waste of fuel arises from a misunderstanding of the 

 nature of a hot-water apparatus, and from an attempt to make it do that 

 which, if it be properly constructed, it is impossible that it should do. 



" It is a great desideratum with gardeners, as far at least as my experience 

 goes, to get up heat in a short time ; and their ordinary test of the excellence 

 of a hot-water apparatus is, how speedily they can get the water to boil. 

 Where an apparatus is properly constructed, this can seldom be effected 

 without a most extravagant waste of fuel. The water in a hot-water ap- 

 paratus, constructed on the most perfect principles, will take as many hours 

 to heat to the boiling point, as the pipes which contain it are inches in dia- 

 meter, and it will also cool in the same ratio. Four-inch pipes will accord- 

 ingly take four hours to reach the temperature of 200° ; and they can be 

 heated to the boiling point in one hour, only by the consumption of four 

 times as much fuel as would suffice if properly applied, or in fact, allowing 

 for the waste of heat by the chimney, which increases under such circum- 

 stances very rapidly, five or six times as much fuel as is really necessary will 

 be consumed by a gardener zealous of the honour of his apparatus. It is of 

 course possible, by having a furnace and boiler excessively large in comparison 

 with the pipes, to construct an apparatus with four-inch pipes which shall 

 boil in an hour ; but the necessary consequence will be that such a furnace 

 would burn during every hour of the night four times as much fuel as can 

 possibly be effective in heating the building to which it is applied. 



" If a house is to be heated rapidly, the pipes should be of the smallest 

 diameter which is consistent with a free circulation ; but it must be borne in 

 mind that such pipes will also cool with equal rapidity ; and, if the heat is to 

 be maintained through the night, the furnace must be so constructed as to 

 contain a large quantity of fuel, but only to allow of a very slow consumption, 

 much after the manner of Dr. Arnott's stove. Now such a furnace, though 

 theoretically very easy, and practically not very difficult of construction, re- 

 quires an almost scientific nicety of management not to be expected from 

 common gardeners. There are, moreover, several objections to small pipes, 

 one of the most material of which is this, that the motion of water within 

 them being retarded by friction in a much greater degree than in large pipes, 

 they can never be brought to so high a mean temperature. So that, under 

 similar circumstances of pressure, &c, 200 ft. of one-inch pipe could never be 

 made to produce the same effect as 50 ft. of four-inch, though their surfaces 

 would be nearly equal ; besides which, the original expense of the one-inch 

 pipe would be nearly three times that of the four-inch. 



" A little consideration will enable us to determine whether such rapid 

 communication of heat be really essential to the efficiency of a heating ap- 

 paratus. In hothouses, where permanent heat is required, it is evidently un- 

 necessary. The only place where it may be desirable is in buildings where 

 occasional heat only is employed. Now if any one will take the trouble to 

 note hourly the variations of the thermometer by night, in weather in which 

 frost is so severe as to be dangerous, they will find that, instead of a sudden 

 jump of 10° or 20°, the thermometer begins to fall slowly an hour before 

 sunset, somewhat more rapidly afterwards, and continues falling steadily till 

 about 1 1 p. m. After that time it falls still more slowly till 3 or 4 a. m., by 

 which time it will have almost reached its minimum. Its variation will be 

 something like 3° or 4° per hour for the first four hours, after that about 1° 

 per hour for the next two or three, and then from i to i of a degree till it 

 has reached its minimum. Now it is evident that to meet this variation, 

 supposing the temperature of the house to range exactly with outer air, an 

 apparatus which occupies three or four hours in reaching its maximum would 

 be much more accurately adapted to the emergency than one which could be 

 heated in an hour. But we may observe that, except in iron-roofed houses, 

 the temperature within the house does not keep pace with that of outer 

 air, but falls much more slowly, owing to the specific heat contained in the 



