38 LETTERS ON NATUBAL MAGIC. 



Isaac Newton, and others, that the imagination 

 has the power of reviving the impressions of 

 highly luminous objects, months and even years 

 after they were first made. From such phenomena, 

 the mind feels it to be no violent transition to 

 pass to those spectral illusions which, in particular 

 states of health, have haunted the most intelli- 

 gent individuals, not only in the broad light of 

 day, but in the very heart of the social circle. 



This curious subject has been so ably and fully 

 treated in your Letters on Demon ology, that it 

 would be presumptuous in me to resume any 

 part of it on which you have even touched ; but 

 as it forms a necessary branch of a Treatise on 

 Natural Magic, and as one of the most remark- 

 able cases on record has come within my own 

 knowledge, I shall make no apology for giving a 

 full account of the different spectral appearances 

 which it embraces, and of adding the results of a 

 series of observations and experiments on which 

 I have been long occupied, with the view of 

 throwing some light on this remarkable class of 

 phenomena. 



A few years ago, I had occasion to spend some 

 days under the same roof with the lady to whose 

 case I have above referred. At that time she had 

 seen no spectral illusions, and was acquainted 

 with the subject only from the interesting volume 

 of Dr. Hibbert. In conversing with her about 

 the cause of these apparitions, I mentioned, that 

 if she should ever see such a thing, she might 

 distinguish a genuine ghost, existing externally, 

 and seen as an external object, from one created 

 by the mind, by merely pressing one eye or 

 straining them both, so as to see objects double ; 



