THE FORCE BEHIND NATURE. 355 



the atmosphere." In these two cases, the mind is the passive 

 recipient of the sensory impressions. But, thii-dly^ when we 

 determinately hft a weight or hold it suspended by our hands, we 

 experience, in addition to the sense of pressure and the sense ot 

 tension, a sense of effort^ which we recognize as an immediate 

 revelation of consciousness, not referrible to any physical im- 

 pression, but of the same kind as that which we experience in 

 a purely mental act, such as the fixation of the attention. And a 

 little consideration will, I think, make it clear that it is on this 

 "sense of effort" in resisting downward pressure, that our cognition 

 of weight is essentially based. 



For, in \}s\q^ first place, the continuance of a moderate pressure on 

 the cutaneous surface, like other sensory impressions that become 

 habitual, soon ceases to affect us sensorially for we cognosce 

 rather the changes in the states of our sense organs, than the states 

 themselves. Or, again, we may suffer under a temporary or per- 

 manent paralysis of the cutaneous sense, that may prevent our 

 feeling the contact of the body we are lifting or supporting; and 

 yet, recognizing its downward pressure in other ways, we can put 

 our muscles into action to antagonize it. But, secondly, this 

 paralysis may extend to the muscular sense, so that the feeling of 

 muscular tension is wanting, as well as that of contact-pressure ; 

 and yet none the less can a weight be lifted or sustained by a 

 conscious effort, provided that the deficiency of the guiding 

 sensations ordinarily derived from the muscle itself is supplied by 

 the sight. A woman whose arm is sensorially but not motorially 

 paralyzed, can hold up her child as long as she looks at it ; and a 

 man affected with the like paralysis of his legs, can stand and 

 walk while looking at his feet. But, thirdly, since the mental 

 sense of effort is experienced in every determinate exercise of our 

 muscular power, and is, as all experience teaches, a necessary 

 condition of that exercise ; since, again, it is proportioned to the 

 exertion we put forth, and continues as long as that exertion is 

 sustained — it is in this, and not in the cutaneous or muscular 

 impressions, which are (so to speak) accidental, that as (it seems to 

 me) we find the real basis of our cognition of the " ponderosity " 

 of matter. 



But " ponderosity " cannot be considered an essential property 

 16 



