440 Jiff. Faraday on the {0B{T« 



But there is another force, independent of that of gravity, at 

 least of the general gravity of the earth, which appears to me 

 sufficient to overcome a certain degree of vaporous elasticity, 

 and consequently competent to the condensation of vapour of 

 inferior tension, even though gravity should be suspended}: I 

 mean the force of homogeneous attraction. 



Into a clean glass tube, about half an inch in diameter, intro- 

 duce a piece of camphor : contract the tube at the lamp about 

 four incnesfrom the extremity ; then exhaust it, and seal it her- 

 metically at the contracted part ; collect the camphor to one end 

 of the tube ; and then, having placed the tube m a convenient 

 position, cool the other end slightly, as by covering it with a 

 piece of bibulous paper preserved in a moist state by a basin of 

 water and thread of cotton ; in this way, a difference in temper- 

 ature of a few degrees will be occasioned between the ends of 

 the tube, and after some days, or a week or two, crystals of 

 camphor will be deposited in the cooled part ; there will not, 

 however, be more than three or four of them, and these will 

 continue to increase in size as long as the experiment is undis- 

 turbed, without the formation of any new crystals, unless the 

 difference of temperature be considerable. 



A little consideration will, I think, satisfy us, that, after the 

 first formation of the crystals in the cooled part, they have the 

 power of diminishing the tension of the vapour of camphor, 

 below that point at which it could have remained unchanged in 

 contact with the glass, or in space : for the vapour of the cam- 

 phor is of a certain tension in the cooled end of the tube, which 

 it can retain in contact with the glass, and therefore it remains 

 unchanged; but which it cannot retain in contact with the 

 crystal of camphor, for there it is condensed, and continually 

 adds to its mass. Now this can only be in consequence of a 

 positive power in the crystal of camphor of attracting other par- 

 ticles to it ; and the phenomena of the experiment are such as 

 to show, that the force is able to overcome a certain degree of 

 elasticity in the surrounding vapour. There is, therefore, no 

 difficulty in conceiving, that by diminishing the temperature of 

 a body and its atmosphere of vapour, the tension of the latter 

 may be so far decreased, as at last to be inferior to the force 

 with which the solid portion, by the attraction of aggregation, 

 draws the particles to it, in which case it would immediately 

 cause the entire condensation of the vapour. 



The preceding experiment may be made with iodine, and 

 many other substances ; and indeed there is no case of distinct 

 crystaUization by sublimation* which does not equally afford 

 evidence of the power of the solid matter to overcome a positive 

 degree of tension in the vapour from which the crystals a^iP 



* CfUomel) conosive gublimftte, oside of aDtimoDy> na^htlialiAe} 02(^ ^i^, Sifi* ^c. 



