2141. The circulation of hot water on the siphon principle appears to have been invented about the same time by Kewley and Fowler, already mentioned; but it was first exemplified by the former engineer, in Colvill's nursery, in 1826. Mr. Fowler took out a patent for his mode in 1829, and some hothouses in Devonshire have since been heated by it. Mr. Kewley's mode has been extensively employed in various parts of the country. We shall describe both.