398 Cambridge Philosophical Society : — 



vated solely by water-action, but owed its origin to one of the lines 

 of disturbance which have fissured this portion of the earth's crust, 

 and that, taking this view of the case, the fissure probably still 

 existed, being merely filled with comparatively loose material, and 

 would prove a serious obstacle to any attempt to drive a sub- 

 marine tunnel which would have to traverse it. 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 

 [Continued from p. 310.] 



May 7, 1855. — The Master of Trinity read a paper on Plato's 

 notion of Dialectic. 



At the end of the survey of the sciences contained in the seventh 

 book of the Republic, which was the subject of a paper at the 

 last meeting, Plato speaks of Dialectic as a still higher element of 

 a philosophical education, fitted to lead men to the knowledge of 

 real existences and of the Supreme Good. Here he describes Dia- 

 lectic by its objects and purpose. In other places Dialectic is spoken 

 of as a method or process of analysis ; as in the ' Phaedrus,' where 

 Socrates describes a good dialectician as one who can divide a subject 

 according to its natural members, and not miss the joint, like a bad 

 carver. Another Dialogue, in which there are examples given of 

 dividing a subject, is the Sophistes, where many examples of dichoto- 

 mous or bifurcate division are given. But this appears from the 

 Dialogue to have been a practice of the Eleatic rather than of the 

 Platonic school. Aristotle proposed a division of subjects according 

 to his ten Categories, which he and others since have extensively used. 

 Xenophon saj's that Socrates derived Dialectic from a term implying 

 to divide a subject into parts, which Mr. Grote thinks unsatisfactory 

 as an etymology, but which has indicated a practical connexion in 

 the Socratic school. The result seems to be, that Plato did not 

 establish any method of analysis of a subject as his Dialectic ; but he 

 conceived that the analytical habits formed by the comprehensive 

 study of the exact sciences, and sharpened by the practice of dia- 

 logue, would lead his students to the knowledge of first principles. 



Also, Mr. Maxwell gave an account of some experiments on the 

 mixture of colours. 



May 21. — A paper was read by Mr. Hopkins on the External 

 Temperature of the Earth and the other Planets of the Solar System. 



We have not sufficient data to determine the superficial tempera- 

 ture of any planet besides our own. We know, however, that it 

 must mainly depend on the temperature of the planetary space, and 

 on the heat which the nearer planets at least receive directly from 

 the sun, but modified, and possibly in a far greater degree than 

 has been generally supposed, by the particular circumstances by 

 which each planet may be characterized. The modifying circum- 

 stances more particularly referred to in this paper, are the existence 

 of atmospheres surrounding the planets, the positions of their axes 

 of rotation, and the conductivity and specific heat of the substances 

 forming the outer crust of each planetary body of our system . No 



