130 Scientific Proceedings, Royal Dublin Society. 
Professor Ogden Rood, in a paper published in the American 
Journal of Science (Silliman’s Journal) for September, 1860, 
first suggested the use of a cobalt-blue glass for seeing the 
phenomenon, which he independently discovered. In a second 
paper, Professor Ogden Rood also gives an approximate measure: 
of the size of the moving corpuscles; assuming them to be close 
to the retina, he found them to be about +,5, of an inch in 
diameter, about twice the size of the red corpuscles of the blood.* 
That the appearance was closely associated with the circulation 
of the blood in the retinal vessels was shown by Dr. Reuben, of 
America, who noticed that there were periodic jets of these bright 
particles which synchronised with the beating of his pulse. He 
considered that the bright appearance was due to the corpuscles 
acting as microscopic lenses condensing the light on the retina.” 
In 1870, Dr. Pope, of New Orleans, drew attention to the fact 
that there appeared to be two classes of these moving corpuscles : 
one a continuous stream of bright specks, and the other whose 
path resembled the letter S; the latter appeared to have a periodic 
movement synchronous with that of the pulse.’ 
Helmholtz states he saw these moving particles, and came to 
the conclusion that they were an agglomeration of blood-corpuscles 
arising from some temporary stoppage or variation in the flow of 
blood through the smaller capillaries in the retina.* 
In order to see the phenomenon clearly, the observer should 
look at a bright sky through one or two thicknesses of cobalt-blue 
glass, the eye being directed to a point some two or three feet 
beyond the glass, the other eye being closed. There will then be 
no difficulty whatever in seeing a succession of rapidly moving 
bright specks, their movement resembling the rapid tossing of balls 
to and fro by a conjurer. A. small streak of light is left behind 
most of them, doubtless due to the persistence of the impression on 
the retina, so that some resemble very fine luminous commas. The 
path of some is like the letter S, and there appears to be no 
cessation in their rapid gyratory and wandering movement. 
1 American Journ. Sci., 1860, vol. xxx., p. 264; and 1861, vol. xxxi., p. 325. 
2 American Journ. Sci., 1860, vol. xxx., p. 38d. 
3 Annales d’ Oculistique, 1870, vol. lxvi., p. 461. 
+ Optique Physiologique, p. 222. 
