I was much pleased with Mr. Poppey's remarks on heating greenhouses with hot water. The paper has some merit if it does no more than induce gardeners to acquire that knowledge that we usually leave to the engineer or machinist; but I thought he might have gone more into details. He says that our modern boiler is only a heater, and in this he may be correct, but I prefer the old name boiler. I am aware that a boiler to generate steam has more surface exposed to the action of fire than a greenhouse boiler, or simply any hot water boiler, as the one has room to store up steam, the other does not require. He says that 2,137 lbs. of coal are used to put one cubic foot of water, at 321/2o into steam. I would wish all my houses were in Guinea, or elsewhere, if I had to consume 1100 lbs. of fuel a day, even in the coldest weather, to a boiler that carries a little over 800 feet of pipe, to keep the water boiling. I would require to fill the pipes frequently, and find many leaky joints next day.

The house the above pipe is in is 30x64, about twelve feet to the apex; keep the house from 65° to over 70°, and use about twenty tons Lehigh coal a season. I prefer to not have the water leave the boiler at 180° and in most of the time less. The boiler may be considered serviceable if the water at furthest from the boiler is 130° to 150°. Some two or three of the other houses are larger and carry from 1,000 to 1,100 feet to give a heat of 00°; they failed in extreme cold weather, and I attached a small boiler to two of them with about 500 feet of pipe to each; now they are safe and I consider this season has nearly paid the extra cost.

Now, we will examine the conical boiler that has so small a surface exposed to the draft. It appears when we look into the fire it heats the water by absorption, and the only piece of iron exposed in the draft is that lump of iron projecting to the center of the fire. It is the first boiler we had in the United States that was really serviceable. All the new inventions that I have seen are not as good as it, and so say those who have several patterns. The only objection is its cost. Many gardeners praise their boilers the first season. Few of them are to be relied on. The man who removes the old brick flue, and replaces it with boiler and pipe, goes into extacies over the change, praises it, is only sorry he was so long troubled with the abominable hot air; now he has ample heat with little care, no sulphur gas, no sitting up on cold nights, gets the snow to melt on his glass nearly as fast as it falls, etc. The second winter a slight change takes place in his thoughts. He is unable to procure the same amount of heat by 4° or 5° as he had the previous winter. Should he lose as much heat every succeeding season, it is not to be relied on, or will be a bill of expense.

This takes place in every apparatus where steam or water is supplied as a medium for heating purposes, and there is no way that I know of to avoid it. Water when heated liberates some neutral salts and alkaline earths, which are deposited on the inside of the pipes, filling up all the interstices in the iron, and reducing their radiating power as stated above. The best preventative is to make allowance when you put the apparatus up.

Having progressed so far in examining Mr. P.'s communication, the remaining points appear to be written for the edification of the editor. However, that may be, the editor has given it to the public, perhaps with the view that some readers would answer some of the questions for the benefit of the readers. Mr. P. puts a question for you or some one to answer; I wish you would answer it. "Has ever any patentee ascertained and informed us of how much heat in his boiler is secured to the water, and how much escapes through the chimney?" To answer the question as it reads, I would say so long as a fire was under the boiler all the heat in the iron goes into the water. However, Mr. P. did not intend to put it that way, and I will call it a slip of the pen. I presume he wants to know how much of the heat from a given amount of fuel is utilized. A patentee said there was no known means of utilizing all the caloric generated. More than half went up the smoke flue and it might be seventy per cent. Experiments by eminent chemists on the locomotive engine show that only ten per cent. of the caloric is utilized; full nine-tenths goes somewhere.

Gardeners not a few have shown me furnaces and flues - they ought to be reliable for every-day nature is their study, and ought to be well read on natural philosophy, well and capable to bring and keep us in the right path - and say all the heat in their fuel produced was used in the house. The philosopher tells us that there is as much fuel used in boiling a ket-tle of water for an old person's breakfast as would generate steam to propel a locomotive one mile. Mr. P. can bring his own deductions on any heater if he has one in use. I think we may get twenty-five per cent. and more, likely less, certainly not thirty, there being so many avenues besides the chimney for its escape. I have no desire to mislead anyone, even though I were a patentee; but there are facts about fuel that every gardener should know is really indispensable, whether they use the hot air flue, steam, water, or any other method. My little experience with gardeners is something curious- they take all the information they receive kindly, but quietly say they don't believe it. It is easy to teach men, but up-hill work to unlearn them. "As the twig is bent, the tree is inclined," is as true now as when it was first promulgated.

Bituminous coal is used to make the gas we burn. 2,000 lbs. produces 10,000 cubic feet of gas. To burn the same to produce a white light without smoke it requires to be supported by two feet of oxygen to each foot of gas. Should one foot of oxygen be used it would produce smoke in abundance, but the two feet of oxygen is required to give it perfect combustion. There is only one-fifth oxygen in the atmosphere and sometimes less, so that 10,000 feet of carburetted hydrogen requires 100,000 feet of atmospheric air to give perfect combustion. Taking in the coke it would use 130,000 feet of air, and probably anthracite coal might require 150,000 cubic feet of air to support a ton weight of such fuel. Suppose you have to use 400 lbs. of coal in one fire, in twenty-four hours you require nearly 2,800 lbs. of air to support the coal. This has to pass through your chimney in the form of carbonic acid gas, and the large bulk of it between three o'clock P. M., and three o'clock, A. M. It is absolutely necessary to give a sharp draft to have a chimney of ample dimensions to carry off the same.

A good draft can be diminished; a poor one can get no increase.

The main piece of advice Mr. P. gives is to examine into the propriety of giving our pipes more radiating surface than a four-inch pipe gives. From it we have eleven inches radiating surface, and twelve inches of water to the inch. With a section of an eight-inch pipe you have to heat twenty-five inches of water. Make it an oval shape and you reduce it to six or eight inches and a summer's work to put the article up. It would quadruple the cost without the shadow of an advantage. Gentlemen are driven from the pleasure of keeping horticultural establishments more on account of their gardeners than on account of love for horses or yachts. Many gardeners treat their employer as if his means were for their own pleasure. No gentleman wants to employ a tormentor. If horticulture is neglected by men of means, many of the gardeners of the present day may lay it as much to their predecessors, chiefly as to any other rival pleasure. Horticulture will increase, and the country be covered with pleasant residences and horticultural grounds when the employe studies the comfort and pleasure of his employer, and not sooner.

Some may think I am putting facts in too strong a light, but no one has a greater desire to see horticulture flourish more earnestly than I.

[Though not authorized to attach the writer's name to his communication, we may say that he has been for many years an employer of gardeners, and that through many discouragements he still keeps up a very interesting greenhouse establishment, and therefore speaks of steam boilers, hot water boilers, and the relation of gardeners to their employers, from actual experience.

In regard to this boiler question, we are not disposed to grant it much space, because the principles can be readily learnt from any elementary work, and the practice is so varied and varies so much in results by incidental circumstances seldom noted by ordinary observers, that very little actual profit comes to the reader. - Ed. G. M].