1 64 SCIENTIFIC RECREATIONS. 



Were it advisable, we could multiply instances. In the Edinburgh 

 Journal of Science these, and many more instances of spectral illusions were 

 narrated by the husband of the lady. She frequently beheld deceased 

 relatives or absent friends, and described their dress and general appearance 

 very minutely. On one occasion she perceived a coach full of skeletons 

 drive up to the door, and noticed spectral dogs and cats (her own pets' like- 

 nesses) in the room, There can be no doubt upon these points ; the 

 appearances were manifest and distinct. They were seen in the presence of 

 other people, in solitude, and in the society of her husband. The lady was 

 in delicate health, and very sensitive. The spectres appeared in daylight as 

 well as in the dark, or by candle-light. 



Let us now, guided by what we have already written, and by Sir David 

 Brewster's experience, endeavour to give a rational explanation of these 

 illusions. " The mind's eye is really the body's eye, and the retina is the 

 common tablet upon which both classes of impressions are painted, and by 

 means of which they receive their visual existence according to the same 

 optical laws." 



" In the healthy state of mind and body the relative intensity of the 

 two classes of impressions on the retina are nicely adjusted the bodily and 

 mental are balanced. The latter are feeble and transient, and in ordinary 

 temperaments are never capable of disturbing or effacing the direct images of 

 visible objects. . . . The mind cannot perform two different functions at 

 the same instant, and the direction of its attention to one of the two classes 

 of impressions necessarily produces the extinction of the other ; but so rapid 

 is the exercise of mental power, that the alternate appearance and dis- 

 appearance of the two contending impressions is no more recognized than 

 the successive observations of external objects during the twinkling of the 

 eyelids." 



We have before illustrated, by means of the pen and the ink-bottle, how 

 one object is lost sight of when the other is attentively regarded, and a 

 material picture or scene may be equally lost sight of, and a mental picture 

 take its place in the eye, when we recall places or people we have seen or 

 remembered. 



We have all heard numerous anecdotes of what is termed "absent- 

 mindedness." Some people are quite absorbed in study, and can see or hear 

 no one in the room when deeply occupied. We may be satisfied then that 

 "pictures of the mind and spectral illusions are equally impressions upon 

 the retina, and only differ in the degree of vividness with which they are 

 seen." If we press our eyes the phosphorescence becomes apparent, and we 

 can make a picture of the sun or a lamp visible for a long time to our 

 closed eyes if we stare at either object for a few seconds, and shut our lids. 

 So by increasing the sensibility of the retina we can obtain the image, and 

 alter its colour by pressure on the eye. 



It is well known that poisons will affect sight, and belladonna applied 

 to the eyes will so affect them as to render the sight nil, by enlargement of 



