230 Cambridge Philosophical Society. 



explanation of the periodic change. He further urges the importance 

 of following up without delay, and in the most effective manner, a 

 branch of the research which gives so fair a promise of establishing, 

 upon the basis of competent experiment, a conclusion of so much 

 theoretical moment. 



In conclusion the author adverts briefly to considerations which 

 may give a particular importance to accurate numerical values of the 

 magnetic elements and their secular changes at Toronto, namely the 

 proximity of that station to one of the two points on the northern 

 hemisphere, which are the centres of the isodynamic loops, and are 

 the points of the greatest intensity of the force (on the surface of 

 the globe) of apparently two magnetic systems, distinguished from 

 each other by the very remarkable difference in the rate of secular 

 change to which the phenomena in each system appear to be subject. 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 

 [Continued from p. 153.] 



March 11, 1850. — On the Knowledge of Body and Space. By 

 H. Wedgwood, M.A. 



No part of the great metaphysical problem chalked out by Locke 

 has been more assiduously laboured, and none has attained a less 

 satisfactory solution, than that which relates to the origin of the 

 idea of space and its subordinate conceptions, figure, position, mag- 

 nitude. 



It was seen that the exercise of the muscular frame must somehow 

 be instrumental in making us acquainted with the material and ex- 

 tended world, but all hopes of a logical explanation of the process 

 by which that effect is produced seemed cut off at the outset by a 

 preliminary objection. The knowledge of motion, it was said, ob- 

 viously involves the knowledge of the body moved. The conscious- 

 ness of the motion of the hand therefore implies the conception of 

 the hand itself, an object of certain shape and size. The attempt 

 to account for the notions of shape and size from the motion of the 

 hand was thus apparently stranded in a hopeless paralogism ; and so 

 insurmountable was the difficulty taken to be, that philosophers were 

 driven to imagine a second source of elementary ideas, in addition 

 to the simple apprehension of the thing conceived in actual existence, 

 maintaining that space is known to us as the condition under which 

 we perceive external things, or. as others express it, that the notion 

 of space arises in the mind on the first apprehension of body by a 

 principle of necessary judgement, which impresses upon us the con- 

 viction that all body is contained in space. 



In the paper laid before the Society, an attempt is made to show 

 the utter barrenness of this hypothesis of a necessary origin (as it is 

 called) of the idea of space ; and the main object of the paper is to 

 rest the idea on a more solid foundation, by showing the adequacy 

 of muscular exertion, in conjunction with the sense of touch, to fur- 

 nish us with complete knowledge of the material and extended world 

 by the ordinary way of actual experience. 



There are two kinds of action; one instinctive, immediately in- 



