136 Scientific Proceedings, Royal Dublin Society. 
of these specks or corpuscles; one set very numerous, moving 
rapidly in small ares of circles, and at the same time having a 
brisk translatory movement across the field of view, the path 
being indefinite and sinuous. The specks of the second class enter 
the field in jets at each beat of the pulse, and describe a path 
somewhat like the letter S, disappearing after having traversed a 
small portion of the field of view. Even without a blue glass, 
T can see these shining specks when a bright sky is looked at. 
Others have also observed the same thing. 
At Professor Barrett’s suggestion I have attempted to measure 
the retinal diameter of these specks, when seen projected on to a 
white surface at a known distance from the eye. But the results 
vary a good deal; the retinal image, and therefore the diameter 
of the corpuscles if they are near the retina, seem to lie between 
the 5,5, to seca of an inch, the latter being minute points of 
light and really not measurable, but the larger measurement may 
be taken as fairly correct. 
