4 SCIENTIFIC THOUGHT. 



mena and properties of natural objects, and the higher 

 ethical problem of fixing upon that which is lastingly 

 real and important in the continuous change of sensation 

 and opinion. The latter formed the central interest of 

 that course of reasoning which began with Socrates and 

 culminated in Plato and Aristotle ; the former was the 

 problem of natural philosophy of which Epicurus and 

 Lucretius stand out as the great representatives. In 

 a well-known passage of the second book of his great 

 poem, Lucretius explains the apparent rest of natural 

 things by the simile of a flock of lustily dancing sheep, 

 which at a distance looks like a white spot on a green 

 hillside/ This tendency of philosophic reasoning to see 

 motion where common-sense only sees rest, to reduce 

 theoretically the apparently permanent properties of 

 things to a play of intricate but imperceptible modes 

 of motion, has governed still more markedly modern 

 scientific thought. I shall comprise all efforts to give 

 more definite " expression to this general idea under 



1 ' De Natura Rerum,' ii. 308— Omnia qute nobis longe eonfusa videntur 



Et velut in viridi candor oonsistere 



"Illud in his rebus non est mirabile, colli." 



quare, 



Omnia cuni rerum primordiasint inmotu, o rpj^j^ ^^^^^ definite expression is 



Sumnia tamen summa videatur stare ; ... . . ', 



quigtg ! entn-ely a que.stion or niatneniatics. 



Prseterquam siquid proprio dat corpora ; It is interesting to note how Le 



™ot"s. , . ^ ., ^aEre, in his ' Lucrece Neutonien ' 



Omms^^en.m longe nostris ab seHsibus ^ ^g^^^.^ ^^^^ ^-gg^^ ..^^.g^^^ ^j^^^ 



Primorum natura jacet ; quapropter, ubi [ if Epicurus bad had but a part of 



the geometrical knowledge of his 

 contemporary Euclid, and concep- 

 tions of cosmography the same as 

 those of many then living, he might 



ipsa 

 Cernere jam nequeas, motus quoque sur- 



pere debent ; 

 Prsesertim cum, qu» possimus cernere, 



celent ^ ^. ^ 



Ssepe tamen motus spatio diducta lo- ; Y^^ye discovCTed the laws of imi- 



Nan?sa"i"'in colli toiidentes pabula l»ta ; versal gravity, and not only _ the 



Lanigerse reptant pecudes quo quamque laws, but, what was the despair of 



vncantes Newton, its mechanical cau.se " 



Invitai.t herb* pemraantes rore recenti, /'ATinirn ' T.noretiu* ' vol ii n 13.5^ 



Et satiati agni ludunt blaudeque coru«- (Munro i^ucretius ^ol u p. i60). 



cant; I Lionardo da Vinci (1452-1519) says : 



