82 PROCEEDINGS OF THE AMERICAN ACADEMY 



point, as the flame of a candle, when we view it with the 

 eyelids nearly closed. He said that until lately he had been 

 accustomed to refer this phenomenon to reflection from the 

 surfaces of the two eyelids, the lower surface reflecting the 

 incident rays upwards through the eye, the upper surface in 

 the opposite direction. From the oblique incidence of the 

 light in each case, the minute irregularities of the surface 

 might be supposed to have the effect, by a linear conjunction 

 of images, of prolonging the picture on the retina, just as the 

 ripples on a lake elongate the image of the moon, or of a burn- 

 ing torch when in a suitable position, so as to form a luminous 

 band stretching over the water from beneath the object nearly 

 to the spectator. A similar explanation has recently been 

 suggested by M. Trouessart in the Compt:;s Re?iclus. 



The seventh number of Poggendorf's Anjialen for the pres- 

 ent year contains a paper on this subject by H. Meyer of 

 Leipsic, in which he refers these vertical beams to refraction. 

 As the eyelids are moved over the eyeball, they gather before 

 them the moisture which continually lubricates the surface of 

 the eye. Owing to the oily secretion of the lids, this moist- 

 ure, instead of spreading on their surface so as to form a con- 

 cavity outwards, is by the opposite capillarity moulded into a 

 converse form, which may be approximately regarded as a 

 quarter-cylinder lying in the angle of junction of each eyelid 

 with the cornea. The light striking the upper of these con- 

 vexities will by refraction be bent upwards through the eye, 

 and that incident on the lower will be bent downwards. In 

 this view, therefore, the upper eyelid is the one concerned in 

 producing the beam which appears vertically under the object, 

 and the lower eyelid in producing that which appears verti- 

 cally over it. But by the hypothesis of reflection the reverse 

 of this must be the case, the beam above the object being 

 due to the action of the upper eyelid, and the opposite beam 

 to the lower eyelid. 



Professor Rogers mentioned a simple experiment, which 

 proves that' the latter cannot be the true explanation, and 



