In going over some back numbers of this magazine, 1 find two articles on the above named subject, one in the February number 1876, page 44, and the other April, 1876, page 106, both intended to throw more light on this matter, which has become a very important means in regard to heating houses; dwellings as well as plant houses. Having mainly to deal with it for gardening purposes, two factors present themselves for our consideration. One is the apparatus, and the other by no means the less important of the two is the manner in which we apply the heat produced from it.

Considering the first, we seem to have come to a stand still. There is a "boiler," a queer looking thing, more or less foolishly constructed, but patented withal, and said to be superior to all others, but in fact only different. My objections to all of them to begin with, are the price of acquisition and the subsequent feeding of them. I do not believe that the result is adequate to the outlay, and it is in the economy of hot water heating where I find ample room for a very desirable improvement, and this in my opinion, ought to come from intelligent gardeners, rather than wait for some enterprising plumber to "hit upon it." That some gardeners say they don't want anything better than X.'s or Y.'s boiler, does not prove that we need not something better, nor might have it. If however, we continue to treat this subject in the usual empirical and not in a truly scientific manner, we will never reach a more satisfactory result than all our "best boilers in the world," duly patented and persitently advertised have given us up to the present time.

Paine says in his •' Common Sense:" "The long habit of not considering a thing to be wrong, gives it the superficial appearance of being right." Does it not appear strange that to heat water, apparently as simple a thing as can be, should call for such a numerous variety of more or less complicated apparatuses, every one of them claiming, like sewing machines, to be superior to its rivals ? Ought this almost endless diversity not to raise the suspicion of their being about as infallible as the M. D.'s and the D. D.'s ? The three "essential points" in a boiler, the first mentioned correspondent enumerates, I cannot indorse as such. For the first, to be capable of burning all kinds of fuel, I cannot see a good reason nor a possibility or a necessity. The second, to have plenty of heating surface, we have best in the boilers in which we actually boil water to make steam, and this is neither surpassed yet nor even reached in any of our so-called boilers, which, in fact, are no boilers at all, but only heaters, and ought to be called so, as we do call the very same thing when the pipes connected with it are filled with air instead of with water.

Permit me here to remark that there are yet too many persons of the opinion that the heat obtained from hot water pipes is moist, whilst that from flues or steam pipes is supposed to be dry. This error, like all errors arising from a want of thinking, might seem pardonable when an Englishman who had been twenty-two years foreman in perhaps, the greatest heating apparatus estab-ment in the United States, entertained that same opinion until I undeceived him. The fact is, we obtain heat from steam filled pipes perhaps many degrees above 212° F., whilst that from hot water pipes is always considerably less than that. But why your correspondent in the April number would not have his water above 160°, he does not say, nor does there seem to be a good reason for it, except it be that for which the fox didn't want the grapes. I think that, especially in cold nights, many a gardener would have been glad to obtain the balance of 52°, if that patented boiler had produced it.

That that point can so seldom be surpassed, is another proof that the boasted boilers are not such perfections as they are claimed to be by the patentees. There is one defect surely, especially in the conical ones, and that is the heating surface. Though there be enough of it, it is too far from the burning fuel, and the heat is expected to act sideways, which it only does to a very small extent by mere absorption, its natural tendency being invariably perpendicularly upwards, acting by penetration. To raise the temperature of the water to the desired degree, it is therefore "essential" that the heater should permit more heat to enter the water than it can lose by absorbtion and radiation. "When a heater does not admit of a fire big enough to secure that effect, then it is too small or ill constructed; if it does, but at too great expense, it is certainly not such a perfection as it is claimed to be. Since the heat when liberated in our ordinary boilers, in its upwards course does never strike immediately and directly a horizontal surface, but heats a considerable volume of air, and most of it will, with the draught, pass through the chimney; and without a draught there is no heat, for the draught supplies oxygen, without which no fuel would burn; and to produce a certain amount of heat, a certain amount of fuel has to be burnt.

Has ever any patentee ascertained and informed us of how much heat in his boiler is secured to the water and how much of it escapes through the chimney? According to Lavoissier, Laplace, etc., 2,138 lbs. of coal of the best quality are required to bring a cubic foot of water at a temperature of 32 1/20 F. to the boiling point. If, therefore, one afflicted with a "rouser" of a patented boiler will ascertain the quantity of water he has to "boil," he can, by keeping an account of the coal he uses, pretty well see how his heater uses him in regard to cost. The next item in this matter is the shape, efficiency and cost of the pipes. Your correspondent says, and so do most of the patentees, "put in plenty of pipe," but they don't say how much that is. One who knows how much a big piece of chalk is, may make a pretty correct calculation, but others will have to guess at it. "We use our heating apparatus only about half the year, the other half it lies there and nobody thinks of it. During the time it is used it suffers very little if at all, but during the time it stands idle the work of destruction, by way of Corrosion, goes on day and night, and its result often becomes visible at a time when we can but ill afford to wait for repairs to be made.

Another item is that we have to be prepared for an extreme, though but short, cold spell, and if we do that, by increasing the extent of pipes, we have too much for the ordinary temperature. The four-inch pipe has been pronounced the best size, because the water to be heated presents a proportionate surface for radiation, whilst in a smaller size is too much surface to the water, and in a larger, too much water for the surface. When this is correct, then a pipe forming a section of a cylinder two inches deep, with a bottom eight inches wide, would without increasing either the quantity of water or the surface of the pipe, both receive and yield the heat faster than a four-inch cylinder. This I would consider an advantage, since there is no radiation downward. It is, moreover, questionable whether cast iron is yet the best and cheapest material for both heater and pipes; these often laid by ignorant mechanics without due regard to their office, and several narrow upright cylinders put up as expansion tanks, with an equal want of judgment, and to finish, a return pipe as long as the flow.

That hot water has some decided advantages over any other means of heating cannot be denied, but that we have not yet arrived at a point in the construction of the apparatus,beyond which there is no possible improvement is equally true.

For forcing fruit, flowers and vegetables, also the cultivation of tropical plants, we have to employ artificial heat, not only to obtain the requisite temperature of the atmosphere, but also and more so to warm the soil, - in gardener's language, to give "bottom heat." In getting heat of the atmosphere as high as wanted, most gardeners have succeeded well enough, but they rarely trouble themselves about the cost, except they have to pay for both apparatus and fuel, and but few seem to pay due attention to the application of the heat to their plants. To this important subject the attention of cultivators, professionals and amateurs must be drawn when we expect an advance in our indoor gardening. As none of our present hot water apparatus is serviceable to that end, gardeners have either to rely yet on horse-dung and tanners' bark, or get along as best they can without bottom heat. Here is a field for gardeners to introduce an important improvement, but I fear that, with the poor encouragement they receive at the present time, they will be slow in bringing on a better system of cultivation than we have, if the growing of the commonest cut-flowers and bedding "stuff" by the hundred thousand may be called cultivation at all.

It is a subject of surprise to Europeans, seeing our well-to-do gentlemen deprived of the enjoyment of gardens for the most part of the year, through the rigor of our climate, take so little interest in the cultivation of beautiful and interesting tropical plants. But they seem to forget that where there is a horse there can't be a palm, and if the promotion of gardening is to be left to the women, it will always be a smallish affair of calla lilies, portulaccas, and such little things. With a climate so unfavorable to the cultivation of most Summer flowers, but on the other hand superior to any other for indoor gardening, it is doubly to be regretted that we find not one of our many rich men taking a pride in assuming the lead in gardening, and thus, either alone or by association, setting an example to the coming generation in the enjoyment of wealth, and showing young America that there are yet more things worthy of a gentleman's interest besides horses, stocks, and yachting.