LETTERS ON NATURAL MAGIC. 



that Friar Bacon walked between two steeples, 

 which was thought to be done by glasses, when 

 he walked upon the ground." 



Kircher also devoted himself to the production 

 of such images, and he has given in the annexed 

 figure his method of producing them. At the 

 bottom of a polished cylindrical vessel A B, he 



Fig. 10. 



placed a figure CD, which we presume must have 

 been highly illuminated from below, and to the 

 spectators who looked into the vessel in an 

 oblique direction there was exhibited an image 

 placed vertically in the air as if it were ascending 

 at the mouth of the vessel. Kircher assures us 

 that he once exhibited in this manner a represen- 

 tation of the Ascension of our Saviour, and that 

 the images were so perfect that the spectators 

 could not be persuaded, till they had attempted 

 to handle them, that they were not real substances. 

 Although Kircher does not mention it, yet it is 

 manifest that the original figure A B must have 



