The Present Limits of Vision. By Dr. Boijston-Pigott. 189 
Eight beads were seen to run together and form three beads. 
Twenty beads counted in one row. Between the rows of red beads 
very small dots visiUe of dark colour. The terminal beads of each 
row are emerald green. 
" Focus slightly lower. Beads green, with darJc round ring 
round each. 
At upper focus. On removal of blue glass shade beads are 
yellowish red ; ground orange colour. 
Description of the Quill. 
^' At lowest focus. Centre, i. e. tube of quill green, with black 
border. White halo. 
" Focus slightly higher. Centre paler green ; border line quite 
black ; halo tinged with pink. 
" Focus slightly higher. Centre pink ; border line deepest black, 
and edged with light green. 
Focus slightly higher. Black lines very sharply defined. 
Centre (of quill) pink beads, eleven or twelve counted. 
" Podura domestica. Under same conditions as on preceding 
day. Scale unbroken. (A different scale chosen.) 
"1. At highest focus. Longitudinal lines of red beads. Beads 
not all of same size.* Ground yellowish green. Some of the beads 
tipped black in centre. The edge of the scale is not a continuous 
membrane, but resembles a twisted rope of the same colour as the 
beads in the interior. The beads are strung together irregularly 
— i. e. the numbers in each string varying. 
" 2. At middle focus. Two distinct sets of beads longitudinal and 
transverse. Beads are of different colour, some dark green, light 
pink, light green, and black : all the beads strung in one group 
are not of the same colour : rouleaux of green, red, and black 
beads principally distributed longitudinally. The form of the 
rouleaux is generally wavy." 
The most remarkable points in these observations made by my 
visitors (one acting as amanuensis) are the beads seen tipped with 
black, the deep black border line, and the dozen pink beads within 
the quill, as also the variation of colours in different focal planes. 
One other thing is worthy of note. " Betiveen the rows of red 
heads very small dots were visible of a dark colour ;" and the ter- 
minal heads of each row were emerald green. 
I need hardly say this perfection of definition is difficult of 
attainment. The most perfect form of definition I have witnessed, 
and still more bafiiing, is to observe six minute dark beads filling up 
* Mr. Browning first pointed out this peculiarity to me at my house in March, 
1869, and alluded to by him in the discussion on the Podura paper same year. 
