be assured that what you take for spots on the sun are the faults of your glasses, or of your eyes.”  The dead hand of Aristotle barred the advance in every department of research.  Physicians would have nothing to do with Harvey’s discoveries about the circulation of the blood.  “Nature is accused of tolerating a vacuum!” exclaimed a priest when Pascal began his experiments on the Puy-de-Dome to show that the column of mercury in a glass tube varied in height with the pressure of the atmosphere.

170.  Desargues’s style of writing. Nevertheless, authority counted for less at this time in Paris than it did in Italy, and the tragedy enacted in Rome when Galileo was forced to deny his inmost convictions at the bidding of a brutal Inquisition could not have been staged in France.  Moreover, in the little company of scientists of which Desargues was a member the utmost liberty of thought and expression was maintained.  One very good reason for the disappearance of the work of Desargues is to be found in his style of writing.  He failed to heed the very good advice given him in a letter from his warm admirer Descartes.(8) “You may have two designs, both very good and very laudable, but which do not require the same method of procedure:  The one is to write for the learned, and show them some new properties of the conic sections which they do not already know; and the other is to write for the curious unlearned, and to do it so that this matter which until now has been understood by only a very few, and which is nevertheless very useful for perspective, for painting, architecture, etc., shall become common and easy to all who wish to study them in your book.  If you have the first idea, then it seems to me that it is necessary to avoid using new terms; for the learned are already accustomed to using those of Apollonius, and will not readily change them for others, though better, and thus yours will serve only to render your demonstrations more difficult, and to turn away your readers from your book.  If you have the second plan in mind, it is certain that your terms, which are French, and conceived with spirit and grace, will be better received by persons not preoccupied with those of the ancients....  But, if you have that intention, you should make of it a great volume; explain it all so fully and so distinctly that those gentlemen who cannot study without yawning; who cannot distress their imaginations enough to grasp a proposition in geometry, nor turn the leaves of a book to look at the letters in a figure, shall find nothing in your discourse more difficult to understand than the description of an enchanted palace in a fairy story.”  The point of these remarks is apparent when we note that Desargues introduced some seventy new terms in his little book, of which only one, involution, has survived.  Curiously enough, this is the one term singled out for the sharpest criticism and ridicule by his reviewer, De Beaugrand.(9) That Descartes knew the character of Desargues’s audience better than he did is also evidenced by the fact that De Beaugrand exhausted his patience in reading the first ten pages of the book.