THE FARMER AT HOME. 203 



feel cold, and to the other hot. Persons ascending from the burning 

 shores of Vera Cruz, on the road to the mountain land of Mexico, will 

 feel the climate become colder, and will put on their great coats, and 

 yet they will meet people descending complaining of the heat. Cold, 

 therefore, is nothing but a negative quality, simply implying the 

 absence of the usual quantity of caloric. 



When gaseous substances become liquid, or liquid substances solid, 

 by this change of state they lose, in a great measure, their capacity 

 for caloric. During the slaking of quicklime, the caloric which is 

 evolved escapes from the water in consequence of its changing from a 

 liquid to a solid form by its union with the lime. When solid bodies 

 become liquid or gaseous, their capacity for caloric is proportionably 

 increased. If you place a glass of water in a mixture of equal quan- 

 tities of snow and salt, during their conversion to a liquid, the water 

 will be frozen in consequence of parting with its caloric to supply the 

 increased capacity of the mixture. The portion of caloric necessary 

 to raise a body to any given temperature is called its specific caloric. 

 The instrument in common use for measuring the temperature of 

 bodies, is called a thermometer. It consists of a glass tube containing 

 a portion of mercury, with a graduated scale annexed to it. 



When a thermometer is brought in contact with any substance, the 

 mercury expands or contracts till it acquires the same temperature ; 

 and the height at which the mercury stands in the tube, indicates the 

 exact temperature of the substance to which it has been applied. It 

 will not show the absolute caloric in substances ; for it cannot measure 

 that portion which is latent, or chemically combined with any body. 

 Caloric is the cause of fluidity in all substances capable of becoming 

 fluid, from the heaviest metal to the lightest gas. It insinuates itself 

 among their particles, and invariably separates them in some measure 

 from each other. Thus ice is converted into water, and by a further 

 portion of caloric, into steam. We have reason to believe that every 

 solid substance on the face of the earth might be converted to a fluid, 

 or even to a vapor or gas, were it submitted to the action of a very 

 high temperature in peculiar circumstances. Some bodies give out 

 their superabundant caloric much sooner than others. Iron is a 

 quicker conductor of caloric than glass, and glass than wood. 



The study of the laws of caloric to the agriculturist, is of great 

 interest and importance. Although some plants can exist with a very 

 small degree of heat, yet some of it is essential to all fluidity, as already 

 stated, and also, of course, to circulation, and consequently without it 

 there can be no growth. The rapidity of all vegetation is in a great 

 measure depending on the degree of heat combined with moisture, to 

 which the plant is subjected, and there are many which cannot exist 

 except in countries and places of high temperature. The effect in 

 forcing the growth of plants may be seen every season in our fields 

 and gardens, and it has been ascertained by actual experiment, that 



