"Hotwater-men," as gardeners term "Horticultural Engineers," do not always know most about heating; and as to boilers, one has only to contemplate some of their misshapen and thoroughly stupid inventions to understand how much they know about their business; but they are not quite so bad as some "judges" of boilers. There are men who have had a large share in awarding valuable prizes to stupid boilers, Who possessed no real knowledge of the subject whatever. There are numbers of common-sense people who have never yet fathomed the mystery of awarding a grand medal to a boiler because it was a common "saddle" squeezed in at the sides to make these perpendicular (a bad fault), and had its inside capacity reduced in order to make two chimneys under the roof of it. Fancy erecting a fireplace in a room with the half of the grate or heating portion of the fire turned to the wall ! What we wish particularly to refer to here, however, is the paper read lately by Mr A. D. Makenzie of Edinburgh on "Economy in Fuel" in garden furnaces. Mr Makenzie's ideas are sound, and simple as well. He prefers a boiler with plenty of internal capacity for fuel, and with a grate-bar wide enough to admit sufficient air to burn it thoroughly.

Any inventor may proceed on these line3. It is not that portion of real manufactured heat going up the chimney, and supposed by some to be lost, which troubles the Edinburgh engineer so much, but the heat that escapes in a latent state - i.e., in the form of smoke and un-burned particles : he wants to burn the "reek," which is just what some of our fine boilers will not do. They are tar-distilling and gas-making apparatus. When the stoker feels his hoe getting sticky with tar as he pushes it under his " water jacket" boilers that boast of " no fire-brick settings" or other aids to perfect combustion, he may then always be sure that his coal is going away bodily up the chimney, or being expended to worse purposes. Listen to what an eminent authority says on this point : " If a fireplace were required to be constructed so as to drive off as much as possible of the hydrogen in an unignited state (that is, to merely waste the fuel), the best plan would be to have the furnace bars and sides formed of pipes with cold water constantly circulating through them.

Those portions of fresh coal which lie against the boiler undergo for some time distillation rather than combustion; and while they are thus wasting they intercept a large portion of the boiler surface from the central portion of the fuel, which is probably in a state of incandescence." . If your readers will apply this test to some of our " double million power," hollow-barred heating apparatus of the present time, it will give them a more accurate conception of their merits. Very wisely, too, does Mr Makenzie tell us that he prefers a long low boiler to a short lofty one, for he has found that with a short boiler he could not raise the same heat as with along one. Plenty of stokers know this from experience.

One of the failings of our boiler-makers is a penchant for adding side and top auxiliary flues, in the belief that they are thereby adding power to the boiler. Neither wings nor top flues should ever be added to a saddle boiler till it becomes so long that you cannot reach the end of it conveniently with the poker. When this happens, and you have any iron to spare, you may use it to make a tail or a wing outside, but not before. You can never get so much heat from an outside flue as you can get from that portion of the boiler which is exposed to the direct action of the fire; and with a long saddle of proportionate width, and set on fire-brick, you may challenge the most complicated or best silver or gold medal boiler ever invented, and feel sure of beating them, provided you know how to stoke.