20 
the results will be as follows. Standard solution 0'8 grams 
in 500 cub. c. of water; length of column 22*5 : 
ABC 
6-400 2-77 6-498 
In this experiment I used the right eye. The theoretical 
length is 2-81, and the above result is therefore a near 
approximation. 
With the same solutions, on the following day (June 26th) 
the results were not so favourable ; the mean of eight trials 
gave 2’57 cm. as the length of the equivalent column, the 
left eye being used in the determinations. On the next 
day (June 27th) I repeated the experiments with these 
solutions, using the right eye ; the mean of four trials gave 
2-8. To each solution I added 5 cub. c. of ammonia, and 
repeated the experiment; the mean of four trials gave 2*13 
as the result. These differences of results are probably due 
to some internal changes in the coloured fluids. 
I may also take this opportunity to correct two numerical 
errors in the sixth volume of the Society’s Memoirs. Page 
262, line 3, for 3-2 read 2-2 ; and on page 264, line 2, for 15 
read 50. 
