Steam is not simple enough, for we cannot trust it to the care of any boy or any laboring man, who does not understand it, without the danger of the steam either condensing or exploding. Whereas an explosion of hot water pipes would be impossible. It would be merely a leak, nothing more and easily stopped. Steam has never proved effectual for horticultural purposes so far as I know or have read, that I can recollect, and has always been given„up wherever tried. Steam may be good for heating large dwelling houses, stores, large halls, factories, etc., but the thin glass structures built for horticultural purposes are altogether another thing. Also, "the disadvantages of steam, as a vehicle for conveying heat to hothouses are few." I hardly dare presume to question the opinions of such authorities as Mr. Loudon, but nevertheles I have opinions and ideas of my own, and think the disadvantages of steam, as compared with hot water are many.

The first disadvantage is, and it is a great one in plant growing, that after making the fire, we get no warmth at all from the pipes until the water in the steam-boiler boils. It then makes steam which heats the pipes all at once, to at least 212° Fah., which is at least 30° too hot for any heating medium for the good of the plants; and no matter how we try to modify the means of heating, by throwing the steam into large boxes of stones, etc., we cannot convey the steam any distance from the boiler without heating the pipes to at least 212°.

Another disadvantage is that if we want to leave our fire nine or ten hours through the night, and after going to bed it should burn out or burn low towards morning, the boiler ceases to make steam, the steam in the pipes is condensed at once, and we cease to get any warmth.

Now, if we should try an experiment in heating two houses, each containing the same number of cubic feet of air, both built alike and glazed alike with the same quality of glass, each house containing, say 300 feet 4-inch pipe, one for water, the other for steam and take a night when the air is still and the mercury at 32° outdoors and in-doors, with a thermometer hanging midway of each house, about four feet from the ground and equal distance from the heating medium, and start the fires both together and note the time it takes to raise the mercury to 00° in each house and the amount of coal it takes. When the mercury has stood at 60° for a short time make up both fires, so as to use the same quantity of coal in each and note the time it takes for each house to cool down to the 32° again. By such means we might come to some definite conclusion as to which is the cheaper and better means, hot water or steam.

I have no doubt the steam will raise the heat to 60° a little the soonest, although the circulation in the hot water pipes will commence the soonest. But the difference in the time of rais-ing the mercury to 60° by each apparatus will not exceed, I think, half an hour, while in cooling down, almost the instant the fire begins to cool down in the steam boiler the water will cease to boil, and of course the steam in the pipes is condensed at once, and there is no warmth given out except what is contained in a mere dribble of water from the condensed steam and what warmth is contained in the iron itself. Now the hotwater pipes, if there be 300 feet of 4-inch diameter, will contain about 200 gallons of water and weigh about 2000 pounds. And it must be apparent that the warmth contained in this body of water will take a longer time to be cooled down to the 32° than the same amount of steam, supposing the water to be heated to 212° the boiling point, the same as the steam.

The steam will cool down more in five minutes than the water in five hours, in a given number of cubic feet of air under like circumstances. A given bulk of water in 212° will contain more than 200 times as much heat as the same bulk of steam at 212°. These figures are, of course, only approximate, but near enough for all practical purposes. To go into exact figures would take a long time and be a great deal of trouble. We have tried the old brick flue, then steam, then hot air or polmaise; then the hot water tank and finally hot water pipes. A great deal more might be said on this subject; but at present, for cleanliness, neatness, compactness, efficiency, durability, safety and economy of fuel and labor, all would be in favor of hot water pipes, 4-inch diameter.

Of course there are many different sizes and forms of pipes, and patterns and forms of boilers, and each has its advocates; but the universal desirable source of artificial warmth for horticultural purposes, for this latitude of our country is from water, apply the heat to the water as you may think best.

And now Mr. Editor, you have made the suggestion of heating horticultural buildings by means of the waste heat of lime kilns. Perhaps it is a good idea, but I perceive you do not advocate the mode very much. We know it can be done, while the lime kilns are kept at work. The waste heat will heat the water, and the water will heat the buildings, provided all things are in proper proportion. But is it desirable? Is it to be recommended? I am inclined to think it is not. There may be times when we wish to make lime and do not desire the heated water in the buildings, and others when we want the warmth, but cannot get the heat up quick enough. As I said before, we know it can be done; but I doubt the desirability of the means for horticultural purposes. As to the "nasty lime market" idea, that might be got over by having the kilns at some distance from the buildings to be heated, and convey the heat by an underground passage entirely out of sight to the buildings. The kilns might be hid by large clumps of shrubbery, etc., and the smoke carried off by an ornamental chimney or pagoda.

And many other ways might suggest themselves.