We are very glad to see that our little article on the heating of greenhouses has at least succeeded in agitating the new, or perhaps more properly, reviving the old idea of the effectiveness of steam in the minds of practical men, such as your correspondent, Mr. Salter; and as we have invited such friendly criticism as his we shall endeavor to the best of our ability, to respond to his queries.

The cubical contents of our establishment which we heat, are about 65,000 feet distributed in several houses - none of which are glazed with double thick glass. The average temperature we require for the stock grown in the houses is about 55°. The number of feet of four inch pipe we use would be of no use as a comparison, as we have considerable direct steam radiation, and we must affirm that we have found the steam quite as efficient, and less expensive than water. The first cost of the steam boiler and connections is about the same as hot water, with many things in favor of the steam boiler.

We perfectly agree with Mr. Salter, that the slow soft warmth obtained from hot water is preferable to overheated mediums, such as flues, but we have yet to discover any baneful effects produced by growing plants in steam heat; and we can but think that the reason why hot water superseded steam in the olden time, was not from any ill effect produced by steam, simply from the incompleteness of the apparatus vised, and its great cost, both of which difficulties have now vanished in our forty years later experience; we therefore still do honor to Mr. Loudon's opinion that steam is both simple and effectual for heating glass structures.

Our fires are attended by the same men who had the care of them under the old regime, and have run them two years without any trouble. Their heads shook dolefully when the steam boilers were being put in, but now they affirm that the apparatus has conquered their prejudices. The fires require to be kept burning the same as a hot water boiler. We have never had to remain by our fires all night; they are generally left from between nine and ten o'clock until seven in the morning. We use an automatic steam damper, which is really the completing part of the apparatus, for without it we could do nothing.

It may be almost too radical to advocate the heating of glass houses altogether by steam, but from what we have seen and know we should not be surprised at any time to learn that some adventurous spirit had " gone and done it "

Whoever does it, and proves the efficiency or deficiency of steam, will deserve a medal from all the Horticultural Societies in the world.

Steam has proved itself the most efficient for heating other structures, - why not for glass houses. 10,000 cubic feet of air to be heated is much the same thing, be it in a church or a conservatory; the only difference being in the amount of radiating surface required.

As to Mr. Salter's difficulties, they do not appear in practice; we consider ourselves as safe with 5 or 10 pounds of steam as we should be with the water boiler. The whole apparatus is built to stand ten times the pressure that we subject it to; therefore our factor of safety is very large. We find that in twenty minutes from the time we build a fire, everything being cold, we can have our steam pipes hot; which certainly is preferable to waiting two or three hours for it. Of course the steam pipes are much hotter than water pipes, but the effect of these very small, very hot pipes is about the same as the moderately warm very large water pipes. The steam heating surface can be distributed over the houses with greater facility than water pipes, and there need be but one third as much of it. In our opinion, Mr. Salter's experiment would prove nothing beyond the fact that, if he were searching for a comparison between hot water and steam, and wished to reach a satisfactory result, he was on the wrong track.

The difference between steam at 212° and water at the same temperature, and under the same pressure would be very little, - in fact, we fail to see how there could be any. We understand what Mr. S. means, but does not express, viz.: that a body of water will retain heat longer than a body of steam; that there is two hundred times as much heat in the water as is in the steam we very much doubt; but one thing is certain, and that is, if Mr. S.'s figures be correct, then it took two hundred times as much fuel to heat the water as it took to make the steam, or to put the heat into the steam.

The whole tiling may be said in a few words. Our creed is as follows, viz.: That it is cheaper to boil a small quantity of water and keep it boiling, than to heat a larger body of water and keep it hot; and some day not in the far future, steam will supersede hot water as a heating medium.

We have combined the two in part of our houses in such a manner that if hot water has any advantages we may have the benefit, and at the same time save in many ways by making our water hot by steam. As yet, we can see nothing in favor of the water, while the advantages of steam are many. By heating a range of houses wholly by steam, the first cost would be much less, as only one-half as much material would be required; it would also be found to be economical in all ways compared with hot water.

Large ranges of glass are now heated by ten or fifteen hot water boilers, some, we believe, requiring more. The whole work can be done by two fires. Think of the time spent running about from place to place looking after the ten or fifteen fires. We are not theorizing; we are merely telling our experience, and Mr. Salter must excuse us if we do not give his theories that attention which they may seem to deserve. Nor do we believe that a greenhouse can be heated without fuel; as, in our estimation, a few tons of coal more or less amount to nothing, so long as we burn it profitably to ourselves. In a well constructed apparatus the more coal that is burned the more heat we should get; and when we have heat enough we can stop the coal supply of the fire. If Mr. S. should happen in Boston we would be happy to show him our steam heating apparatus, and shall hope to be able to convert him to the true faith.

P. S. - Since writing the above we have received the August number of the Gardener's Monthly, and wish to say that Mr. Bochman is the " adventurous spirit," and we wish to take his hand through the G. M.