SPECTRAL ILLUSIONS. 121 



tion to pass to those spectral illusions which, in particular 

 states of health, have haunted the most intelligent indi- 

 viduals, 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 Demonology, that it would be presump- 

 tuous 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 dif- 

 ferent 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 distin- 

 guish 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 ; for in this case the external object or supposed 

 apparition would invariably be doubled, while the impres- 

 sion on the retina created by the mind would remain 

 single. This observation recurred to her mind when she 

 unfortunately became subject to the same illusions ; but 

 she was too well acquainted with their nature to require 

 any such evidence of their mental origin ; and the state of 

 agitation which generally accompanies them- seems to 

 have prevented her from making the experiment as a 

 matter of curiosity. 



