lxxii 
PROCEEDINGS. 
The party then, by permission of Mr. S. Taprell Holland, visited 
the adjacent grounds of Otterspool. The house was at one time, 
perhaps originally, an inn, to which persons resorted in order to 
drink from the famous pool in the days when “ drinking the 
waters” was a fashionable craze. Prior to 1812 the road to 
Aldenham passed between the house and the river, and the existing 
house and beautiful gardens on the banks of the Colne were the 
work of the Thellussons of Aldenham Abbey. The pool, which is 
upwards of twenty feet deep, is perfectly clear, and the water 
appears of a tine blue colour. Mr. Hopkinson explained that this 
colour is due to its purity, as is the blue colour of the air in a clear 
sky; this is not because either pure water or pure air are blue, for 
they are colourless ; it is because blue is the least refrangible of the 
rays of which white light is composed, and so when white light is 
reflected through a pure medium, the blue rays are the last to 
suffer absorption by refraction, the red rays first disappearing (to 
this the green colour of the sea is due), and then the yellow, 
leaving only the blue. He stated that the source of this spring had 
been ascribed to swallow-holes in the Chalk near Radlett, and 
although, as the late Rev. J. C. Clutterbuck had placed on record, 
there were stories of ducks having disappeared down one of these 
swallow-holes, reappearing in this pool, he thought it to be more 
likely that the water flowed out of fissures in the Chalk which 
extended for a long distance, gathering in their ramifications the 
rain-water falling over a large area. In Yorkshire the course of 
underground channels had been traced by colouring the water with 
fluorescein, and he would much like the experiment to be tried 
with our Hertfordshire swallow-holes when they are in action 
after heavy rain. 
The purity of the water in this spring appeared to have been 
unaffected by the recent rains, or, if it had been (for the water is 
sometimes turbid), the effect had very quickly passed off. Hot so, 
it may be confidently affirmed, will the pleasurable recollection of 
those who took part in this interesting meeting. 
