2130. For aquatic plants. Fig. 624. shows a mode of warming a cistern or reservoir of water for the preservation of aquatic plants. Steam is admitted by a pipe, three quarters of an inch in diameter, having perforations of about one tenth of an inch at each foot in length; the extremity of the pipe being closed, the steam issues through the small apertures, filling the whole internal area of the large pipe in which it is enclosed, and imparting an equable temperature to the whole extent of surface. This effect cannot be obtained by applying steam in the common way, when but a small increase of temperature is required; as the water immediately in contact with the pipe where the steam is admitted would absorb nearly the whole of its heat, till it arrived at a temperature far beyond what could be allowed in a case of this kind. The dimensions of the reservoir alluded to, are about 3 ft. by 3 ft. 6 in., and 20 ft. long. The external pipe is 4 in. inside in diameter, and the condensed water from it is taken away by a small inverted siphon (b) at the farther end.