I^^ch National TnsUluie. 187 



tested, some reflections upon the precision necessan,'^ to ob- 

 tain from it all that may Ue expected, will not, perhaps,, be 

 out of place. 



The astronomers ought to be imitated in every particular, 

 who do not content themselves with vaguely attributing the 

 celestial phaenomena to attraction, bat they analyse these 

 phaenomena, showing and distinguishing the parts of the 

 attractions of each of the various bodies, and determining 

 thfe measure and the laws of their action; they explain, by 

 means of a rigorous calculation and precise observations, that 

 these laws are in fact constantly the same, and belong to no 

 arbitrary supposition. 



There is really no meaning in saying simply that living 

 bodies have a vital principle, and in attributing to this prin- 

 ciple every thing we cannot explain by other means. To 

 think that we have said something useful, when we say 

 vaguely, that sensibility and contractibility are effects of the 

 vital principle, in our opinion is both deceiving ourselves 

 and others by an expression devoid of meaning. 



In order legitimately to compare the employment of the 

 attraction with that of universal gravitation, it would be ne- 

 cessary to analyse separately every phcenomenon of life ; 

 to determine the share which the ordinary laws of physics 

 and chemistry have in them ; and afterwards to compare the 

 elements of the phasnomcna which these two sciences could 

 not have furnished, to those which would have remained 

 after the analysis of the other phasnomena ; to sec if all these 

 unknown elements, extracted, if we may be allowed the ex- 

 pression, each one separately from the various phenomena, 

 have any thing conunon among them ; lastly, to ascertain 

 the laws to which we are to attribute their common prin- 

 ciple, if we find that it exists, since, on combining it with 

 those of the ordinary sciences, it gives a rational explanation 

 of all the phaenomena observed, and enables us to foretell 

 with some exactitude the phaenomena which would happen 

 in new circumstances. It is then only that physiology may 

 flatter itself with possessing a particular principle, as well as 

 aiitronomv ; it is then only thai we shall be permitted logi- 

 cally to employ the vital prlncibte in reasonings and calcula- 

 4 tioiii^, 



