354 



SCIENTIFIC THOUGHT. 



rnents of Richer, Halley, and many others, the measure- 

 ments of the arc of the meridian, and Cavendish's and 

 Maskelyne's experiments, were some of the direct results 

 of the discovery. 



It was natural that, having explained the cosmical, and 

 subsequently many terrestrial phenomena, successfully by 

 the formula of attraction, Newton himself, and still more 

 Laplace and his school, should have attempted the ex- 

 planation of molecular phenomena by similar methods. 



The astronomical view spread into molar and molecular 

 physics. Xewton himself made use of the notion of 



81. 



Astronomi- 

 cal view of 

 molecular 



phenomena, molecular attraction ] i.e., of attraction existing only at 



1 In the fourteenth section of 

 the first book of the ' Principia ' 

 Newton is however careful to speak 

 always of " attractio vel impulsus," 

 leaving it open to the reader to 

 form his own opinion whether it is 

 an action at a distance or a " vis a 

 tergo," a push. He says also that 

 the particles of light approaching 

 solid bodies with a definite velo- 

 city are bent, " quasi attracti in 

 eadem (i.e., corpora)." And in the 

 twenty - third query to the first 

 Latin edition of the ' Opticks ' 

 (1706) he says: "May not the 

 small particles of bodies have cer- 

 tain virtues, powers, or forces by 

 which they act at some distance, 

 not only on the rays of light, re- 

 flecting, refracting, or inflecting 

 them, but also on each other, pro- 

 ducing various natural phenomena ? 

 For it is sufficiently known that 

 bodies mutually act on each other 

 through the attraction of gravity 

 and through magnetic and electric 

 virtue. And these examples show 

 what is the order and reason of 

 nature, so that it becomes very 

 probable that there may be other 

 attractive forces. For nature is 

 very similar and agreeing to her- 



self. Through what efficient cause 

 these attractions are brought about 

 I do not inquire here. What I 

 here call attraction may well be 

 produced by an impulse or in some 

 other way unknown to us. I take 

 this word attraction here in this 

 way, that it be understood merely 

 to mean some universal force with 

 which bodies try to approach each 

 other, whatever cause this force 

 may have to be attributed to. For 

 from the phenomena of nature it 

 behoves us first to be taught which 

 bodies attract each other, and what 

 are the laws and properties of this 

 attraction, before we inquire by 

 what efficient cause this attraction 

 is brought about. The attraction 

 of gravity and of the magnetic and 

 electric virtue extend to sufficiently 

 large distances, so that they fall 

 under the notice of the vulgar 

 senses ; but it may be that there 

 are others which are contained in 

 such narrow limits that they have 

 so far escaped all observation." 

 And he goes on to speak of the de- 

 liquescence of some salts and of 

 chemical combinations of finely 

 powdered substances. And fur- 

 ther on in the same query, after 



