of Edinburgh, Session 1881-82. 
637 
4. Note on the Absorption of Sea- Water. 
By Mr. John Aitken. 
In a letter to Professor Tait, dated Mentone, 14th April 1882, Mr. 
Aitken says : — 
Since coming here this time, I have tested the sea with the 
polariscope and with the spectroscope. With an instrument by 
Hoffman, which gives coloured bands with polarized light, I have 
been able to detect small, but decided indications of polarization 
in the light internally reflected by the water, the surface reflection 
being, of course, cut off when the observation was made. At 
present I think the polarization is due to regular reflection from the 
polished surfaces of some of the particles, which are seen to glance 
brightly in concentrated sunlight. 
I have also detected an absorption band in the green of the 
spectrum of the light internally reflected by the Mediterranean 
water. This band is much more distinct in water where there are 
but few reflecting particles, and the light undergoes a great amount 
of selective absorption. At about a mile from shore, where I could 
see a white surface 6 inches square at a depth of 16 metres, the 
absorption band was quite distinct, but became less and less as I 
approached the shore, where there was more matter in suspension 
and the water less transparent, but the spectrum more brilliant. I 
cannot say whether this band belongs to water or to salt, or to what 
it is due, never having noticed it before; but I never examined 
water so transparent, and where the light had undergone so much 
absorption. 
PRIVATE BUSINESS. 
Dr. David Pryde, Mr. J. W. Inglis, Mr. E. W. Young, and Mr. 
T. R. Buchanan, M.P., were balloted for, and declared duly elected 
Eellows of the Society. 
