THOMSON AKO TAIT'S NATURAL PHILOSOPHY. 



M thonxMrhlT ee the whole of that surface of a body which ia turned 

 if indeed, we are not prepared to assert that we have seen the' 

 da too. when after all, if our attention were to leave a trace behind 



a. 0* point of the blind man's stick might do, this trace would appear 

 M men line meandering over the surface in various directions, but leaving 

 between iU convolutions unexplored areas, the sura of which is still equal to 

 whole surface. We are at liberty no doubt to course over the surface and 

 > subdivide the meshes of the network of lines in which we envelope it, and 

 to conclude that there cannot be a hole in it of more than a certain diameter, 

 bat no amount of investigation will warrant the conclusion, which nevertheless 

 we dimw at once and without a scruple, that the surface is absolutely con- 

 tinuous and has no hole in it at all. Even when, in a dark night, a flash 

 of lightning discloses instantaneously a whole landscape with trees and buildings, 

 we discover these things not at once, but by perusing at our leisure the 

 picture which the sudden flash has photographed on our retina. 



The reason why the phenomena of motion have been so long refused a 

 place among the most universal and elementary subjects of instruction seems 

 to be, that we have been relying too much on symbols and diagrams, to the 

 neglect of the vital processes of sensation and thought. 



It is no doubt much easier to represent in a diagram or a picture the 

 instantaneous relations of things coexisting in space than to illustrate in a full 

 and complete manner the simplest case of motion. When we have drawn our 

 diagram it remains on the paper, and the student may run his mind over the 

 lines in any order which pleases him. But when we are either perceiving 

 real motions, or thinking about them without the aid or the encumbrance of 

 a diagram, the mind is carried along the actual course of the motion, in a 

 manner far more easy and natural than when it is rushing indiscriminately 

 hither ami thither along the lines of a diagram. 



Having pursued kinematics from its elementary principles till its intricacies 

 .begin to be appalling, we resume the study of the elements of science in the 

 opening of the chapter on " Dynamical Laws and Principles." It is here that 

 we first have to deal with something which claims the title of Matter, and 

 our authors, one of whom never misses an opportunity of denouncing meta- 

 physical reasoning, except when he has occasion to expound the peculiarities 

 of the Unconditioned, make the following somewhat pusillanimous statement : 



cannot, of course, give a definition of Matter which will satisfy the 



