220 VARIOUS METHODS OF HEATING DESCRIBED IN DETAIL. 



what may hereafter be effected by it, by the friction of one idea 

 against another in the course of experience. For small pits, 

 filled with young stock, it is invaluable, as a pipe may be car- 

 ried from a boiler, heating other structures, into a pit near by ; 

 and, these being easily covered at night, a sufficiency of heat 

 may thus be conducted into them to keep the plants safe 

 during the winter, without much increase of fuel, or any with- 

 drawal of heat from the structure for which the apparatus was 

 originally constructed. Green-houses are generally too much 

 crowded in winter, and the adoption of dry pits for the conserva- 

 tion of plants that are somewhat hardy in their nature, is riot 

 so common as it ought to be. Pits might be so arranged 

 as to obtain the superfluous heating power from other houses. 

 This, in some instances, has been done, and it is likely that 

 more will ere long be done in the same way ; for if the vast 

 amount of fuel, consumed by the general methods of heating, 

 could be economically applied, without waste, it is not exaggera- 

 tion to say that at least one third could be saved. 



The hygrometrical and ammoniacal condition of the atmos- 

 phere of hot-houses has not received that attention, in connec- 

 tion with heating, which the importance of the matter evidently 

 demands. We have books enough teaching us the effects of 

 certain volatile and subtile fluids upon vegetable life, and exhib- 

 iting a multitude of facts which no person will venture to dis- 

 pute ; yet, in this matter, we practicals have, in a great measure, 

 been deaf to the teachings of science, and blind to the lessons 

 of nature. Practically, or experimentally, we have made but 

 little inquiry whether invigorating or contaminating gases 

 abounded in our hot-houses. Now, nature is either a good or 

 a bad teacher, just in proportion as our knowledge of her im- 

 mutable laws is limited or comprehensive. When we confine 

 plants in a case of glass, as in a green-house, if we give them 

 soil to grow in and water to drink, we are apt to think they 

 ought to be contented ; and if they do not thrive well and prove 

 productive, we call them ungrateful, or very difficult to rear. 

 Now, we ought to consider that plants feed by their leaves as 

 well as by their roots, and that the volume of air in which the 

 leaves are expanded, requires to be as regularly moistened and 



