472 
Proceedings of the Royal Society 
distincte sed leviter prominens formantia, dimidiata, depresso-hemi- 
sphserica, mm. lata, basi autem in sectione T 6 0 mm. lata ; para- 
physes tenues, laxe clathratim ramosse ; sporse in ascis 2-8-nse, 
hyalinae, 25 /x longse, 4-10 fx latse, 4-5-septatse, loculi 1-3-locellati. 
• — Ramulicolum : B.C.S. et Scliweinf. 
Bathelium yelatum, Mull . Arg ., thallus vix nisi hyphemoideus 
circa perithecia; stromata suborbicularia, 1J-2 mm. lata, depresso- 
hemisphserica, vertice velata ; peritliecia immersa, dimidiata, basi 
inflexa ; paraphyses connexse, sporse in ascis 1-8, liyalinse, 25-38 
fx longse, 10-15 fx latse, 6-8-loculares, loculi 2-3-locellati. — Corti 
colum : B.C.S. 
There was laid on the table a Note on the Constitution of 
the Lines forming the Low Temperature Spectrum of Oxygen, 
by Professor Piazzi Smyth, Astronomer Royal for Scotland. 
Monday , §th February 1882. 
Professor BALFOUR, Vice-President, in the Chair. 
The following Communications were read 
1. On the Colour of the Mediterranean and other Waters. 
By Mr. John Aitken. 
{Abstract.) 
The investigation was at first undertaken with a view of determin- 
ing how the blue colour of the water of the Mediterranean is 
produced, and of finding the explanation of the different colour 
phenomena seen in that sea. The investigation was afterwards 
extended to other waters. 
The experiments were made with a special view of determining 
whether the selective reflection or the selective absorption theory 
gave the correct explanation of the blueness seen in water. 
According to the selective reflection theory the colour is due to 
the light reflected by extremely small particles of matter suspended 
