42 



Mr Bateson, On the perceptions 



[Feb. 10, 



i.e. in this case the total acceleration, is made up of a com- 

 ponent ra transverse to the radius vector and a component rco 2 

 Therefore the resultant acceleration is 



towards the origin 



o 



(a) 4 + 6?f r, 



and it acts at a constant inclination a to the r; 

 is given by tana=&)/&) 2 ; a known theorem. 

 Thus if / denote the instantaneous centre of 

 the motion, /' this centre of accelerations, and 

 P any point, so that 



IP = r, i'P=p, lpl' = 0, 



we have, by the theorem of centripetal ac- 

 celeration, 



lius vector, which 



Kg. 3. 



therefore 



(co 4 + 6> 2 f p sin {6 - a) = 

 r 2 sin a 



R 



R = 



p sin (6 — a) ' 



The points whose paths have zero curvature are given by 6 = a, 

 and therefore lie on a circle through / and /', the circle of in- 

 flexions. 



Let this circle cut PI in Q ; then 



p sin (0 — a) = PQ sin a, 



therefore E = IP 2 /PQ. 



February 10, 1890. 

 Professor Babington, Vice-President, in the Chair. 



The following Communications were made to the Society : 



(1) On the perceptions and modes of feeding of fishes. By 

 W. Bateson, M.A., St John's College. 



In the course of observations made at Plymouth and elsewhere 

 it appeared that the majority of Fishes are diurnal in their habits 

 and seek their food by sight, but that a minority are almost 

 entirely nocturnal and hunt by scent. To the latter class belong 

 Protopterus, Skates and Rays, the Rough Dogfish, Sterlet, Eel, 

 Conger, Rocklings, Loaches, Soles, &c. These creatures remain 

 buried or hidden by day but career about at night in search of 

 food, returning to their own places at dawn. If while they are 



