160 OF SLEEP. SECT. XVIII. 13 



a fufpenfion of all voluntary power. But if the ideas thus pre- 

 fented to us, iritereft our attention, and are accompanied with fo 

 much pleafurable or painful fenfation as to excite our voluntary 

 exertion at the fame time, reverie is the confequence. Hence 

 an intereding play produces reverie, a tedious one produces fleep ; 

 in the latter we become exhausted by attention, and are not ex- 

 cited to any voluntary exertion, and therefore fleep ? in the 

 former we are excited by fome emotion, which prevents by its 

 pain the fufpenfion of volition, and in as much as it intereds us, 

 induces reverie, as explained in the next Section. 



But when our fleep is imperfect, as when we have determin- 

 ed to rife in half an hour, time appears longer to us than in 

 mod other fituations. Here our folicitude not to overfleep the 

 determined time induces us in this imperfect fleep to compare 

 the quick changes of imagined fcenery with the parts of time or 

 place, they would have taken up, had they real exiftence ; and 

 that more frequently than in our waking hours ; and hence the 

 time appears longer to us : and I make no doubt, but the per- 

 mitted time appears long to a man going to the gallows, as the 

 fear of its quick lapfe will make him think frequently about it. 



13. As we gain our knowledge of time by comparing the 

 prefent fcenery with the pad and future, and of place by com- 

 paring the fituations of objects with each other ; fo we gain our 

 idea of confcioufnefs by comparing ourfelves with the fcenery 

 around us ; and of identity by comparing our prefent confciouf- 

 nefs with our pad confcioufnefs : as we never think of time or 

 place, but when we make the comparifons above mentioned, fo 

 we never think of confcioufnefs, but when we compare our own 

 exiftence with that of other objects ; nor of identity, but when 

 we compare our prefent and our pad confcioufnefs. Hence the 

 confcioufnefs of our own exidence, and of our identity, is owing 

 to a voluntary exertion of our minds ; and on that account in 

 our complete dreams we neither meafure time, are furprifed at 

 the fudden changes of place, nor attend to our own exidence, or 

 identity \ becaufe our power of volition is fufpended. But all 

 theie circumdances are more or lefs obfervable in our incom- 

 plete ones ' 9 for then we attend a little to the lapfe of time, and 

 the changes of place, and to our own exidence ; and even to 

 our identity of peribn ; for a lady feldom dreams, that (he is a 

 foldier ; nor a man, that he is brought to bed. 



14. As long as our fenfations only excite their fenfual mo- 

 tions, or ideas, our fleep continues found ; but as foon as they 

 excite defires or averfions, our fleep becomes imperfect ; and 

 when that defire or averfion is fo drong, as to produce voluntary 

 motions, we begin to awake ; the larger muicles of the body are 



brought 



