"I have two admonitions more to the ingenuous, and well-disposed reader. First that he would not slight my endeavors because of my years, which are but few. It is the custom of most men to measure knowledge by the beard, but look thou rather on the Soul, an essence of that Nature, que ad perfectionem suam curricula temporis non defiderat. Secondly, that he would not conclude any thing rashly concerning the subject of this art, for it is a principle not easily apprehended. p. 69"