INDISTINCTNESS OF IDEAS. 261 



perceive that, if they considered the weight of the 

 body as a power acting to produce motion, they 

 must consider the body itself as offering a resist- 

 ance to motion ; and that the effect must depend 

 on the proportion of the power to the resistance ; 

 in short, they had no clear idea of accelerating 

 force. This defect runs through all their mecha- 

 nical speculations, and renders them entirely value- 

 less. 



We may exemplify the same confusion of 

 thought on mechanical subjects in writers of a less 

 technical character. Thus, if men had any distinct 

 idea of mechanical action, they could not have 

 accepted for a moment the fable of the Echineis 

 or Remora, a little fish which was said to be able 

 to stop a large ship merely by sticking to it. 

 Lucan 1 refers to this legend in a poetical manner, 

 and notices this creature only in bringing together 

 a collection of monstrosities ; but Pliny relates the 

 tale gravely, and moralizes upon it after his man- 

 ner. " What," he cries 2 , " is more violent than 

 the sea and the winds? what, a greater work of 

 art than a ship ? Yet one little fish (the Echineis) 



1 Lucan is describing one of the poetical compounds intro- 

 duced in incantations. 



Hue quicquid foetu genuit Natura sinistro 



Miscetur : non spuma canum quibus unda tiniori est, 



Viscera non lyncis, non durae nodus hyasnas 



Defuit, et cervi pasti serpente medullas ; 



Non puppes retinens, Euro tendente rudentes 



In mediis Echineis aquis, oculique draconum. 



Etc. Fhttrxalia, iv. (>70. 



- Plin. Hist. N. xxxii. 1 



