ia THE PHILOSOPHY 



tion of pleafure and pain, is the principle that regulates all the vital 

 or involuntary motions of animals. To afcertain this point, would 

 require a fet of very nice experiments. I fhall mention one, which 

 might be performed with tolerable eafe. It was formerly remarked, 

 that plants kept in a hot-houfe, where the degree of heat is uniform, 

 never fail to fleep during the night. This is direct evidence, that 

 heat alone is not the caufe of their vigilance. But they are deprived 

 of light. Let, therefore, a ftrong artificial light, without increafmg 

 the heat, be thrown upon them. If, notwithftanding this light, the 

 plants are not roufed, but continue to fleep as ufual, then it may be 

 prefumed that their organs, like thofe of animals, are not only irri- 

 table, but require the reparation of fome invigorating influence 

 which they have lofl: while awake, by the agitations of the air and 

 the fun's rays, by the adl of growing, or by fome other latent caufe. 



It Is almofl: unnecefl!ary to mark the difl:in(3:ion between vegetables 

 and minerals. The tranfition from the animal to the plant is ef- 

 fedled by (hades fo imperceptible, as to elude the moft acute ob- 

 fervers. But, between the plant and the mineral, there is a vaft 

 chafm in the chain of being, which' may be the fource of great dif- 

 coveries. In bodies purely mineral, not a veftige of organization 

 can be difcovcred. The fibrous ftrudure of the afbeftos has been 

 regarded as an approach toward organization, and as the link which 

 conneds the mineral to the vegetable kingdom. But this is one of 

 thofe {trained analogies which are too often employed by theoretical 

 writers. Though the afbeftos is compofed of a kind of threads or 

 fibres, thefe fibres are not tubular ; neither are they interwoven, 

 like that regular tiflTue or fabric which fo remarkably difl:inguifhes 

 organized from brute matter. Of courfe, the magnitude of the 

 afbeftos can only be increafed by the appofition of new matter, and 

 not by any developement or expanfion of parts. But though, in 



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