QUALIFICATIONS OF THE EXPERIMENTER
You must know, my dear friend, that whoever wishes to experiment, should
be acquainted with the nature of things, and should not be ignorant of
the motion of the celestial bodies. He must also be skilful in
manipulation in order that, by means of this stone, he may produce these
marvelous effects. Through his own industry he can, to some extent,
indeed, correct the errors that a mathematician would inevitably make if
he were lacking in dexterity. Besides, in such occult experimentation,
great skill is required, for very frequently without it the desired
result cannot be obtained, because there are many things in the domain
of reason which demand this manual dexterity.