THE PERCEPTION OF THINGS. 93 



hedges, streams, and the like, which break up the interven- 

 ing space and make us the better realize the latter's extent. 

 Both these causes make the moon seem more distant from 

 us when it is low ; and as its visual angle grows no less, we 

 deem that it must be a larger body, and we so perceive it. 

 It looks particularly enormous when it comes up directly 

 behind some well-known large object, as a house or tree, 

 distant enough to subtend an angle no larger than that of 

 the moon itself.* 



The feeling of accommodation also gives rise to false per- 

 ceptions of size. Usually we accommodate our eyes for an 

 object as it ajjproaches us. Usually under these circum- 

 stances the object throws a larger retinal image. But 

 believing the object to remain the same, we make allowance 

 for this and treat the entire eye-feeling which we receive 

 as significant of nothing but approach. When we relax our 

 accommodation and at the same time the retinal imaee 

 grows smaller, the probable cause is always a receding 

 object. The moment we put on convex glasses, however, 

 the accommodation relaxes, but the retinal image grows 

 larger instead of less. This is what would happen if our 

 object, whilst receding, grew. Such a probable object we 

 accordingly perceive, though with a certain vacillation as 

 to the recession, for the growth in apparent size is also a 

 probable sign of approach, and is at moments interpreted 

 accordingly. — Atropin paralyzes the muscles of accommo- 

 dation. It is possible to get a dose which will weaken 

 these muscles without laming them altogether. When a 

 known near object is then looked at we have to make the 

 same voluntary strain to accommodate, as if it were a great 

 deal nearer ; but as its retinal image is not enlarged in pro- 

 portion to this suggested approach, we deem that it must 

 have grown smaller than usual. In consequence of this 

 so-called micropsy, Aiibert relates that he saw a man ap- 

 parently no larger than a photograph. But the small size 

 again made the man seem farther oflf. The real distance 



* Cf. Berkeley's Theory of Vision, §§ 67-79 ; Helmholtz : Physiologische 

 Optik, pp. 630-1 ; Lechalas iu Reuve Philosophique, xxvi. 49. 



