Page:The Amateur's Greenhouse and Conservatory.djvu/22

16 to the circulation of the blood in the body—the fuel is the food, the fire is the life, the boiler is the heart, the flow pipe the aorta, and its ramifications the arteries; the return pipe is the vena cava and its ramifications the veins.

In making a selection of a boiler it is of the utmost importance to ensure greater power than will be required under ordinary circumstances, and in the case of an extensive range of houses there should be two boilers, and they should be in use alternately during periods of a month or so at a time. In case of an accident to one of them—and the best boilers will at times break down—there is another ready for use, and with all



connections complete, so that the turning of a valve and the lighting of a fire are sufficient to save the plants from destruction. We have seen a collection of plants, valued at some thousands of pounds, destroyed through the breaking down of a boiler in a season of intense frost, and at a moment of festivity when no one was prepared for such an emergency.

The simplest form of boiler for a small house is the Upright Conical, which consists of a furnace communicating with an upright chimney through the boiler, which is an upright cylinder not necessarily of a &ldquo;conical&rdquo; form. This may be used without any brick setting, but is far more serviceable with setting than without it, because of the great power of brickwork to prevent waste of heat. One great advantage of this form