August 9, 1901.] 



SCIENCE. 



221 



tainment of either orthoscopic or pseudoscopic 

 binocular effects was described by Sir David 

 Brewster as long ago as 1844 {Edinhurg Trans- 

 actions, 1844, Vol. XV., Part III., p. 360), and 

 quite fully discussed in his book on ' The 

 Stereoscope,' published in 1856. On the op- 

 tical illusions due to cross vision Brewster based 

 his geometric theory of binocular vision, which 

 was fully elaborated in his book. In 1855 and 

 1856 the same theory was applied by Professor 

 W. B. Rogers, founder of the Massachusetts 

 Institute of Technology, in a series of articles 

 published in the American Journal of Science. 

 It has since been applied by various writers. 

 The incorrectness of this theory is conclusively 

 proved by the possibility of-binocular vision by 

 optic divergence {Am. Jour. Science, Nov. and 

 Dec, 1881, March, April, May, Oct. and Nov., 

 1882). 



Nevertheless, the subject is attractive, and 

 the results attainable when the visual lines are 

 made to cross at a high angle, such as 50° or 

 60°, suggest some interesting and perfectly 

 legitimate geometric applications. But these 

 experiments are somewhat trying to the muscles 

 of the eyes. 



W. Le Conte Stevens. 



"Washington and Lee University, 

 August 3, 1901. 



SHORTER ARTICLES. 

 ADAPTATION IN VISION. 



Apparently no one has noticed formally the 

 bearing upon brain ]3hysiology of one of the 

 commonest phenomena of vision. Within cer- 

 tain very wide limits the percept we have of 

 any object does not change at all while we 

 approach or recede from it. If, for instance, I 

 look at a chair thirty feet off and then walk 

 straight toward it, the appearance of the chair 

 does not alter. Now the retinal elements ex- 

 cited are totally diflferent according to the dis- 

 tance I am from the object. We have then a 

 succession of different physiological processes 

 in the retina with the final result in conscious- 

 ness of a constant feeling. We naturally sup- 

 pose that a continuance of the same feeling is 

 due to a continuance of substantially the same 

 physiological processes in the central nervous 

 system. If this is true we can account for the 



phenomenon mentioned only by supposing that 

 all the differing successive processes in the 

 end organ somehow get shunted into the same 

 central process. This involves a practical in- 

 finitude of associative systems of the subtlest 

 and most complex sort. For with each of the 

 objects of which we thus have a constant per- 

 ception in spite of varying retinal conditions, 

 different sets of associations are needed corre- 

 sponding to different views of the object. 

 Moreover, totally new objects suffer like treat- 

 ment. This latter fact almost tempts one to 

 put faith in a mysterious mental construction 

 on the basis of sense stimuli. Surely if the 

 brain itself does the work of unifying these 

 multitudes of series of retinal events into con- 

 stant processes corresponding to our percepts, 

 the complexity of its mechanism has never been 

 fairly stated. This, I take it, is what we must 

 believe. We must find in this commonest case 

 of vision a notable example of the fact that our 

 feelings do not parallel outside events or even 

 the sensory processes aroused by them, but are 

 the results of selected adaptations, adaptations 

 in this case presupposing much more involved 

 neural action than the common reflex-arc con- 

 ception of the brain seems to permit. 



Edward L. Thorndike. 

 Teachers College, Columbia University. 



THE injury of FUNGICIDES TO PEACH 

 FOLIAGE. 



The writer has devoted several seasons to an 

 investigation of the injury produced by fungi- 

 cides to peach foliage. A bulletin giving the 

 results of this work is soon to appear from the 

 Tennessee Agricultural Experiment Station. 

 A preliminary report on this investigation may 

 not be out of place here. Following are some 

 of the points established or rendered probable : 



1. Pure copper hydroxide, copper oxide, or 

 even metallic copper spread on the leaves is 

 injurious to the foliage of the peach, but with- 

 out visible injury to that of either the apple or 

 the grape. 



2. A solution of copper sulphate 0.00005 

 normal ( = 0.000795 per cent.) proved fatal to 

 water cultures of the apple, while grapes and 

 peaches under like conditions, though evidently 

 injured, soon recovered, and the peaches thus 



