There is a curious old book, “The Gardener’s Dictionary,” by Philip Miller, the fourth edition of which was published in 1754. He gives an account of greenhouses and conservatories as places usually unheated. “I suppose,” says he, “many people will be surprised to see me direct the making of flues under a greenhouse; but though perhaps it may happen that there will be no necessity to make any fires in them for two or three years together, yet in very hard winters they will prove extremely useful.” But when the author comes to hothouses, he describes them under the name of “_stoves_.” [Illustration: _Fig. 22._--EARTHENWARE OVEN AS IN USE AT PRESENT.] The stove is a hot chamber, heated maybe by an oven, but we have turned the name about, and we apply it mistakenly to the heating apparatus. In Germany the room that is heated is the _stube_, but the heater is the _ofen_. The _ofen_ is, however, itself a reproduction in small of the hot chamber. The oven is employed to radiate outwards in heating a room; it radiates inwards when employed for baking. The German _ofen_, or, as we would term it, stove, is an earthenware vessel in a room. A fire is lighted in it, till it is thoroughly heated. Then the fire is allowed to expire, and the damper is turned, effectually closing the flue. Thenceforth all the heat within and in the earthenware walls radiates into the apartment, and keeps it warm for eight or nine hours. In the ancient oven, as in the bee-hive huts at Trewortha, every precaution was adopted to retain the heat. The outside was banked up with peat, and the heat gathered within baked bread or meat. The bee-hive oven of courses of stone was not all that could be desired. The fire acted on the granite or limestone or slate, and split or crumbled it, and when one or two stones gave way, the whole dome collapsed.