Nearly as much bosli is said and written on the subject of heating buildings as upon the subject of ventilation. In fact, the subjects are so intimately related, that it is almost impossible to consider them separately. We believe that the whole subject has been too elaborately treated by those who, in aiming to be ultra scientific, have failed to be practical. There are four classes of heating apparatus which have had moreor less favor, and some of which have been very generally used, viz.: Open fires in [grates or fire places, inclosed fires (including the whole generation of coal, wood, and gas stoves), steam heaters, and hot air furnaces. Of all the devices which the evil genius of invention ever put into the head of man to destroy health and comfort, we believe hot air heaters to be the very worst. Nothing but the utmost care, joined to the best constitution, can prevent an army of ills from subduing the health of those exposed to tbe influences of these agents of destruction. We speak from knowledge, having had a large experience in their workings, and the opinions we here express, are based upon sound science, it is almost impossible (the experience of those who have had the management of hot-air furnaces will bear us out in this), to so adjust them that an equable temperature can be maintained in any large building. They are most sensitive to external winds, which, as all acquainted with the subject know, influence, to a great extent, the supply of air from without. Even if vaned hoods be placed over the external openings, which admit the vital fluid, it will at once be seen that the vaiying strength of a wind, blowing from any direction, will render the supply fitful. But this is not the only, nor the worst evil, attending the use of hot-air furnaces. Recent researches have established, beyond a doubt, that external warmth should be received by radiation; and that any method of warming the body by contact of its surface with a heated fluid] is defective and sure to be attended by evil consequences. Leeds, in his lecture on ventilation, says : " Convected heat is the great curse of the American people. It isthat dry, lifeless, withering, debilitating, poisoned stuff with which most of our best houses and public buildings, and, most unfortunately, many of our school houses, too, are filled and warmed, and which is filling our systems, and warming and drying all the life and substance out of about two-thirds of the people of this country." The same lecturer points out that the lower the temperature of the air we inhale, the more readily and copiously the lungs eliminate carbonic acid, and the languor and depression we feel, on a hot summer day, is attributed to this cause. In the hot-air system of warming, the surface of the body cannot be kept comfortable unless the air be maintained at a temperature much higher than necessary when radiant heat is used. Professor Silliman has also pointed out that the combustion of organic matter which the air contains, partially unfits it for breathing, which adds to the category of charges against this most irrational way of heating rooms. Bad as the system is, gas stoves are worse; at least such as provide no escape for the gases of combustion. They may, perhaps, be admissible in summer for culinary purposes, when doors and windows are opened wide, but we should as soon think of sleeping in an apartment connected by an open pipe with the nearest sewer, as in a close room warmed by a gas-stove. There remain stov.es, and steam apparatus, and grates or fire places, to which, in the order named, we prefix the adjectives good, better, best. A great hue and cry have been raised over the effects of stoves upon health. While we admit they have faults of both a positive and negative character, we believe these faults have been much over-rated. It must be confessed, however, that cast-iron stoves are open to the charge of not fully imprisoning the poisonous gases of combustion, while in other respects, they leave much to be desired. It is doubtful, however, whether anything will be devised that, for all classes of people, in all conditions of life, could take the place of the cast-iron stove. Steam heaters, although not so good as open grates or fire places, come so near perfection, when properly constructed, that, when the consideration of their adaptability to heating large buildings is taken into account, they may be said to be the best of all the means yet invented for general heating purposes. They are deservedly popular, but the highest ideal of comfort, health, and cheerfulness in a heating apparatus seems to us inseparable from the open fire, with its cheerful glow, and its outward draft, which sucks in and devours all poisonous exhalations. It makes dust in a room, and this provokes good housekeepers to wrath, but, upon our own temper, we have found its effects to be most bland.