276 NOTICE OF A VISIT TO PITMASTON. 



sures the purity of the air ; and if the latter should enter cold 

 and drj^, it will become comparatively warm and moist before 

 its introduction to the conservatory ; as its temperature is pro- 

 gressively increased in its passage, so will likewise be its capacity 

 for moisture, and this the evaporation of the water will abund- 

 antly supply. 



It is to be regretted, that all the data necessary to estimate 

 the full amount of heat afforded by the above arrangement have 

 not been obtained. Such would have comprised the temperature 

 of the water in the drain, close to the conservatory ; its tem- 

 perature at the farther extremity, just before its egress into the 

 open air ; the temperatures maintained in the conservatory when 

 in communication with the drain, and when the latter was cut 

 off; and the relation which both these bear to the external cold ; 

 and, finally, the exact dimensions of the drain, and the quantity 

 of water discharged by it per minute. 



It is known that the temperature of spring- water differs little, 

 either in summer or in winter, from the mean temperature of the 

 climate. That of the Society's Garden, whicli may be consi- 

 dered similar to the climate of many other places having the 

 same, or nearly the same latitude and elevation, is between 49° 

 and 50', on an average of 22 years. Supposing, however, that 

 spring-water is only of the temperature of 48°, the width of the 

 drain 3 feet, and depth of water 2 inches over the bottom of 

 the drain ; and that the water lost one degree of heat per mi- 

 nute. I have ascertained that the above depth of water will 

 lose as much as one degree per minute when the water is 

 30° warmer than the air to which it is exposed, even with very 

 little wind at the time. Hood states in his Treatise on Heating, 

 that a cubic foot of water in cooling one degree gives out as 

 nnich iieat as would raise 2990 cubic feet of air one degree. 

 Then a drain 70 yards, or 210 feet in length, and 3 feet wide, 

 would have a bottom area of 630 feet ; and 2 inches deep of 

 water over this would give 105 cubic feet, and this quantity of 

 water, according to the above data, by losing one degree of its 

 heat, would raise 313,950 cubic feet of air one degree, or 

 10,465 feet thirty degrees. It has been calculated that one 

 square foot of glass will cool 1'279 cubic feet of air under it 

 one degree per minute, when the external temperature is one 

 degree lower than the internal. Hence, the above 10,465 cubic 

 feet would maintain the air under 8182 square feet of glass as 

 much as 30° above the temperature of the external air, or sup- 

 posing the latter to be as low as 16* Fahr., a conservatory 

 having a surface of glass equal to 8182 square feet would be 

 kept at 46°, provided the full heating effect could be brought to 

 bear upon it. 



