the difference in temperature is greatest between the point of

departure and the extremity of the pipes. What do we re- quire, then, to obtain a good result ? That the water in the pipes obtains as quickly as possible the temperature required, and preserves it for the longest possible time. The Thermo- stat-Thermosiphon realises these conditions."

Lastly, we are bound to mention Musgrave's Slow Com- bustion Stove, which is a stove simply, and not a boiler. It merits mention, because it is the only thing of its kind we would, without fear, place inside a plant house. It must be understood that we do not recommend either the introduction of a gas-flame or a fire of any kind into the same enclosure with any kind of plants, but it is our business to provide for a variety of circumstances, and it is with pleasure we are en- abled to testify, from observation and experience, that Mus- grave's stove is the least harmful amongst many contrivances recommended for placing inside a plant house, and at the same time easily managed, economical, and efficient, as a diffuser of beat. It is manufactured by Messrs. Musgrave Brothers, High Street, Belfast, and the prices range from 90s. upwards, ac- cording to size. For a house of one hundred to two or three hundred square feet of surface or more, this stove may be em- ployed with safety, and in the case of a large house two or three stoves of small size would be more useful than a single large one. A 90s. stove will suffice for a house measuring twenty-five or thirty feet by eight or ten feet wide, but for any smaller sized house it is not suitable at all. The small upright charcoal stoves that are often used to protect miniature green- houses are Defter than nothing if carefully managed, and that is all that can be safely said about them.

Mr. Rothney submits, for the amusement of those readers of this work who are inclined to speculations in engineering, the subjoined plan of a self-acting Thermostat. The descrip- tion is as follows :

The expansive effects of heat on liquids is well known. Water when heated expands in the following ratio : — At 40° it is at its greatest density ; at 65° it increases ^^^ part ; at 100°, -jljj part ; at 140°, X part ; at 180°, J-^ part ; at 212°, -^■j part. This being the case, we have a power which can be applied for regulating the temperature in hothouses, by causing the hot water in the pipes to remain at or not increase above a certain temperature desired, also at the same time storing up