Having for a number of years studied the question of economically heating incubators and chambers for hatching germs, I have been obliged to give a great deal of attention to the subject of boilers and hot-water pipes. The experience gained was always in favor of a reduction of the quantity of water and an increase of heating surface. Working on in this direction I arrived at the result of a half annular pipe instead of the usual system of annular piping. These half annular or *' crescent" pipes, as I have called them, are somewhat on the principle of a saddle boiler, and the small heating apparatus which I have as yet constructed on this principle have fulfilled my most sanguine expectations. A 7-feet length of ordinary 6-inch annular piping contains 8 1/2 gallons of water, whereas my crescent pipes, same length and same heating surface, contain only 5 pints of water. The obvious economy of heating power is a great gain, as it enables me to make heating apparatus sufficiently powerful for any small-sized greenhouse ; this can be worked by an oil lamp, costing from 9d. to 1s. 6d. per week, according to number and length of pipes. So many amateur gardeners object to the trouble attendant upon coke or coal furnaces that I get constantly asked for such a heating apparatus.

Again, the action of the heat is so rapid that notime is lost, and the quantity of water required to be heated is, as before described, very small in proportion compared to that necessary for heating an annular pipe. Another advantage to be gained by these pipes is, that at the unions the pipes can be reversed, and they form excellent evaporating tanks for water where moisture is required. I may say that it is the opinion of manufacturers experienced in hot-water piping that this form is very likely to become general, in hothouses at any rate. Lengths of these can easily be inserted with the ordinary circular pipes. - Thomas Christy, in Gardeners" Chronicle.

Half-annular.

Annular.