text:  And only consider to what procedures profoundly contradictory it immediately conducts! On the other hand they recommend you to isolate yourself as much as possible from all external sensation; and above all they interdict you every intellectual exercise; for if you were merely occupied in making the most simple calculation what would become of your _internal_ observation? On the other hand after having thus by dint of many precautions attained to a perfect state of intellectual slumber you are to occupy yourself in contemplating the operations passing in your mind--while there is no longer any thing passing there