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Proceedings of the Royal Society 
refuses to flow,, and remains aggregated in oil-drops over the 
surface. When the glass in the proximity of one of these drops is 
heated, the oil is seen to creep away from the heated part, leaving 
behind it no trace of oil on the surface. 
3. On “ Tait’s Property of the Eetina.” 
By George Forbes, Esq. 
Professor Tait having asked me to communicate to the Society 
some experiments I have made from time to time on the property 
of the retina discovered by him, and communicated to this Society, 
15th January 1872, I prepared the following notes. It will be 
remembered that he pointed out that when the eye has been rested 
for a long time the first impression of light gives a red colour. 
Professor Crum Brown stated at the same meeting, that after Pro- 
fessor Tait had told him of the appearance he had himself observed 
a like phenomenon. Awaking one morning at grey dawn, and 
opening his eyes suddenly, he saw a glare of red on the window, 
and was so struck by it that he hastily rose to discover what house 
was on fire. 
The circumstances under which Professor Tait made the obser- 
vation were as follows : — He was suffering from sleepless nights 
owing to the illness arising from re-vaccination. He found that at 
each time of awaking, a portion of the wall feebly illuminated by 
a gas-flame appeared to have a crimson hue, and acquired its true 
white colour only after a few seconds of time. 
I have very little to tell the Society, except to corroborate the 
evidence of Professor Tait, and to describe a method of observa- 
tion that removes the necessity for re-vaccination or even sleepless 
nights. I have reproduced the appearance, I suppose, thirty times 
during the past winter. I lower the gas until there is only a 
small blue flame. This may be done before going to bed, and the 
experiment made in the morning, provided the window is darkened 
by shutters. In the morning, on suddenly turning up the 'gas, 
either the gas-flame assumes the crimson flush, or if there be a 
globe of ground glass on the gas, that globe assumes the hue. If 
the gas he quickly lowered again, a short rest is sufficient before 
repeating the experiment. It is never necessary (in my case) to 
