606 SLEEP. 



summer, early study is equally convenient ; and those who have 

 acquired the habit of night study have only to persevere in 

 retiring early, and rising at a fixed. x early hour, and they will 

 after a time find the morning sun tell better than the midnight 

 oil. Some commit the error of rising very early, without going to 

 bed proportionally soon : and the result is of course the same as 

 if they sat up late and rose at ordinary hours ; they go about 

 weak, feverish, and stupid the whole day, and are absolutely 

 knocked up in the evening. 



The effect of too little sleep upon the face is very striking : 

 sailors, who have their rest broken at short intervals, acquire an 

 old look. 



The power of habit over sleep is very great. Within certain 

 limits it will lessen or augment the amount of sleep necessary ; 

 but these limits differ constitutionally in different individuals, and 

 must be influenced by the habitual amount of exertion. Any 

 one may acquire the habit of dividing his sleep, so as to take less 

 at night, and a portion previously in the day or evening. Some 

 become accustomed to have their rest broken at short intervals, 

 and able to sleep directly they wish : they acquire the habit 

 also of waking on the least noise ; that is, of sleeping very lightly. 

 " Seamen and soldiers on duty sleep when they will and wake 

 when they will. The Emperor Napoleon was a striking instance 

 of this. Captain Barclay, when performing his extraordinary 

 feat of walking a mile an hour for a thousand successive hours, 

 obtained at last such a mastery over himself, that he fell asleep 

 the moment he lay down." By habit we wake invariably at a 

 certain hour, however late we may retire ; until, by repeatedly 

 retiring late, the system greatly feels the want of rest : on the 

 other hand, a person accustomed to go to sleep at a certain hour, 

 may oversleep himself in the morning, but becomes drowsy at his 

 usual time in the evening. Habit enables us to sleep in un- 

 favourable circumstances. " An old artilleryman often enjoys 

 tranquil repose while the cannon are thundering around him : 

 an engineer has been known to fall asleep within a boiler, while 

 his fellows were beating it on the outside with their ponderous 

 hammers; and the repose of a miller is no wise incommoded by 

 the noise of his mill." " It is- common for carriers to sleep on 



Dr. Macnish. 



