296 BROOKS. [Vol. X. 



The sensation of weight comes to us in a thousand ways, by 

 the aid of all our sense organs, and without the intervention of 

 any of them. We never lose our consciousness of weight 

 except in the delirium of nightmare, and it is so hard to im- 

 agine its absence that the perception of space is usually con- 

 sidered a necessary condition of mind. 



While all animals are ponderable bodies, the sensation of 

 weight is not due to weight but to specific gravity, to the differ- 

 ence between the weight of the body, or some part of the body, 

 and that of its environment, and if the body be homogeneous, 

 and its specific gravity approximate to zero, there can be little 

 consciousness of weight, or perception of that difference between 

 upwards and downwards and sideways, without which I find 

 myself unable to conceive of voluntary motion or an external 

 world. 



Sight and hearing, no doubt, involve the conception of space, 

 and no conscious animal which sees or hears can be without 

 space-relations ; although we may lose sight, hearing, and even 

 the tactile sense without losing our grasp on the external 

 world. If with these the sense of weight were also lost the 

 world around us would become 



" A great vacuity, a dark, illimitable ocean without bound, 

 Without dimensions; where length, breadth and height, 

 And time and place are lost." 



Now, while I do not assert that the medusae are conscious 

 animals, they are beyond question endowed with the power of 

 spontaneous motion, a power which could not be called into 

 exercise unless movement brought about some change in ex- 

 ternal stimuli. If all the sensations are the same whether an 

 animal moves or not, why should it move .-* 



In the simple world of a jelly-fish the most important 

 diversity is at the surface or the bottom and its movements 

 are in some way adjusted to this relation. 



Now if by any means top or bottom could be fixed all other 

 dimensions of space would also be determined. 



We can imagine two ways of fixing these points by special 

 senses. 



