POTATOES FOR 1849. 277 



Count Rumford, however, estimates much lower the amount 

 of heat which would be communicated to air by the cooling of 

 water. He states, that a cubic foot of water in cooling one 

 degree would give out as much lieat as would raise the tem- 

 perature of a stratum of air over it, and 44 times as thick as 

 the water, 10°. This is equivalent to heating 440 feet one 

 degree. According to this, instead of 10,465 cubic feet, only 

 1540 would be heated 30° per minute, a quantity sufficient to 

 maintain that number of degrees above the external air under 

 no more than 1204 square feet of glass ; still this would be 

 equal to the heating of a moderate-sized conservatory, even in 

 very severe weather. 



Although enough of heat may be generated in the manner 

 described, yet the great difficulty is its conveyance into the 

 interior of the conservatory, and the disposal of the vehicle 

 after it has parted with its heat, namely, the disposal of, say 

 1540 cubic feet of air per minute. This would require for its 

 introduction a velocity of nearly two miles an hour through a 

 passage 3 feet square ; and this is more than the diiference of 

 temperature at the warm and cold ends of the drain would en- 

 sure. It is true, a very small stove adapted to act near the 

 upper end of the drain would powerfully assist the draught ; and 

 when introduced, a considerable portion of air would constantly 

 escape by the openings of tlie glazing. In fact, according to 

 the old mode, the spaces between the laps would be amply suffi- 

 cient ; and perhaps there are cases in which that mode of glazing 

 would prove the best for the health of the plants. In the ar- 

 rangement under consideration it might be adopted with advan- 

 tage ; for by this arrangement air would be continually passing 

 outwards by the spaces, tending to pi'event the rush of cold air 

 inwards, which such spaces were justly complained of for ad- 

 mitting, in severe weather more especially. 



The calculations given in the course of the above remarks 

 are necessarily imperfect ; yet they may serve to induce experi- 

 ments on the subject, by which correct data may be afforded, and 

 important results will doubtless be derived from such ; for the 

 dark green foliage, and excellent condition in every respect of 

 the orange-trees in the conservatory at Pitmaston, warrant this 

 expectation. 



XXXIII.— Po^a^oe^ /or 1849. By R. Errington, Gardener to 

 Sir Philip de Malpas Grey Egerton, Bart., M.P., F.H.S. 



(Communicated August 26, 1848.) 



If there is one fact well established in the history of the potato 

 disease, it is this — that, under present circumstances, early kinds. 



