ON SENSOR1AL VISION. 



having gone so far in this direction, I may perhaps be 

 borne with if I add one or two more observations of a 

 similar personal nature, which, though not bearing on 

 the subject hitherto spoken of, seem to me not without 

 some interest as contributions to that mass of unaccount- 

 able or difficultly explicable facts with which the history 

 of vision teems so abundantly. 



(18.) The first of these is one of constant occurrence 

 to myself in railway travelling. When looking out on a 

 sloping bank, the train going rapidly, if the sight be 

 directed fixedly out in one direction, all near objects 

 stones, grass tufts, &c., are of course seen as if drawn 

 out into horizontal lines. Now what I constantly per- 

 ceive is the appearance of slender obscure lines like 

 dimly seen dark wires at regular intervals asunder, cross- 

 ing those linear streaky images nearly at right angles, 

 and which always seem not to stand vertically up and 

 down, but as if they reclined backwards on the slope of 

 the bank. I find it best to let the eyes take their own 

 focus without endeavouring to adjust them to any 

 object. 



(19.) It is generally taken for granted that to see any 

 object whatever, the best way is to look straight at it, 

 and get its image impressed on the centre of the retina. 

 This is certainly, however, not the case with a single 

 bright luminous point, if no brighter than a star of the 

 third or fourth magnitude, as any body may convince 

 himself by trying the experiment the first clear night. 

 When two such stars of equal magnitude, within a 

 degree or two of each other, are looked at, nothing is 



