Though artisans may not be able at once to execute the invention which is explained in the Dioptrics, I do not think that any one on that account is entitled to condemn it; for since address and practice are required in order so to make and adjust the machines described by me as not to overlook the smallest particular, I should not be less astonished if they succeeded on the first attempt than if a person were in one day to become an accomplished performer on the guitar, by merely having excellent sheets of music set up before him.
At that point, the subject can mentally ( left brain) associate the sensations experienced with the result achieved and can begin to emphasize, by memory recall, the same process to cause its strengthening by affirmation and repetition.
For example, if the subject wishes to increase the circulation in the left leg in order to speed up healing he may concentrate with his left brain on achieving that result while carefully monitoring a digital thermometer connected to the left leg.