B7 



CONTENTS. 



LETTER I. 



Extent and interest of the subject Science employed by 

 ancient governments to deceive and enslave their subjects 

 Influence of the supernatural upon ignorant minds 

 Means employed by the ancient magicians to establish 

 their authority Derived from a knowledge of the pheno- 

 mena of Nature From the influence of narcotic drugs 

 upon the victims of their delusion From every branch of 

 science Acoustics Hydrostatics Mechanics Optics 

 M. Salverte's work on the occult sciences Object of 

 the following letters Page 1 



LETTER II. 



The eye the most important of our organs Popular descrip- 

 tion of it The eye is the most fertile source of mental 

 illusions Disappearance of objects when their images fall 

 upon the base of the optic nerve Disappearance of ob- 

 jects when seen obliquely Deceptions arising from view- 

 ing objects in a faint light Luminous figures created by 

 pressure on the eye, either from external causes or from 

 the fulness of the blood-vessels Ocular spectra or acci- 

 dental colours Remarkable effects produced by intense 

 light Influence of the imagination in viewing these 

 spectra Remarkable illusion produced by this affection 

 of the eye Duration of impressions of light on the eye 

 Thaumatrope Improvements upon it suggested Dis- 

 appearance of halves of objects or of one of two persons 

 Insensibility of the eye to particular colours Remark- 

 able optical illusion described .... 8 



