“Women, like children, require more sleep normally than men, but ‘Macfarlane states that they can better bear the loss of sleep, and most physicians will agree with him.’”  
H. Campbell.
 
The amount of sleep, like the amount of food, required by an individual varies greatly, depending largely upon the conditions at the time. Edison, for instance, can go days without sleep when in some invention, and he has been quoted as saying that people sleep too much, four hours daily being quite sufficient.
 
In answer to my , Mr. Edison’s secretary wrote, “Mr. Edison directs me to write you that the statement is correct, that for thirty years he did not get four hours of sleep per day.” Evidently, experience taught him that an average of four hours per day, if taken rightly and at the right time, is enough for him. He keeps a couch in his workroom so as to sleep when he is sleepy. He does not need a clock to tell him when to go to bed, any more than you need a thermometer to tell you when to pull up the blankets.