PROCEEDINGS OF THE SOCIETY. 
137 
was employed. It was necessary to remain in tlie darkened room for 
five or ten minutes before tlie eye became sufficiently accustomed to the 
conditions, but there was no difficulty in seeing the lines afterwards. 
For opticians’ purposes it would be well to select a sunshiny day, and 
with the help of a heliostat there would be no difficulty in the matter. 
Mr. T. Comber asked if they were to understand that in most lenses 
it was so difficult to correct for the violet ray that this was seldom done ? 
When they remembered that a photograph was practically taken by that 
ray it appeared to him to be very important to those who used the 
lenses for photographic purposes that the violet ray should be properly 
corrected. 
Mr. Gifford asked if Mr. Beck would define what he meant by the 
violet ray. 
Mr. Beck said he meant that portion of the spectrum about H, or the 
H line chiefly. G was very easily seen, and there was not much trouble 
to half-way between G and H, but H was very difficult. 
Mr. Gifford said he could get through all up to H, but not beyond ; 
what he would recommend would be line G. 
Mr. J. E. Ingpen thought personal equation must enter largely into 
a question of this kind. There were many cases in which persons were 
affected with yellow crystalline lens, and this considerably altered their 
appreciation of colour at the violet end of the spectrum. In his own 
case he found this to be very marked, but after the operation he under- 
went he found that his appreciation of the blue end was largely in 
excess of that of most persons, and he certainly saw much farther into 
violet than was usually possible. This power gradually became less 
until at the present time his perception of colour was nearly normal. 
Mr. B. Smith asked if there was any difference in the focus with and 
without the screen ? 
Mr. Gifford said there would be no difference in the case of the 
malachite-green, but there would be with violet. 
Mr. Nelson said that in using a dark-v.'sion spectroscope the light 
ceased at a particular line, but the moment he put on a methyl-blue 
screen then the spectrum shot out considerably beyond that line. 
Mr. Gifford said there was no doubt about this being experienced, 
but he suggested that it might after all be a case in which the eye had 
been fatigued. 
The President thought that the amount of discussion which this paper 
had evoked proved the interest which had been taken in the subject. 
He trusted Mr. Gifford would continue to pursue his investigations in 
this direction, as there could be no doubt as to their importance. 
The thanks of the Society were voted to Mr. Gifford for his paper. 
Dr. Dallinger stated that the Society had the right to nominate one 
student to work at a table at the Marine Biological Association’s 
Laboratory at Plymouth for one month till the 31st of May next. 
The President said that as their next meeting would be their Annual 
Meeting, it was necessary on the present occasion to appoint two Fellows 
•as Auditors of the accounts. On behalf of the Council he appointed 
