.' Were
water of uniform density perfectly free from suspended matter, it
would, in my opinion, scatter no light at all. The track of a
luminous beam could not be seen in such water. But 'an amount of
impurity so infinitesimal as to be scarcely expressible in numbers,
and the individual particles of which are so small as wholly to elude
the microscope, may, when examined by the method alluded to, produce
not only sensible, but striking, effects upon the eye.'

The results of the examination of nineteen bottles filled at various
places between Gibraltar and Spithead, are here tabulated:

No. Locality Colour of Sea Appearance in Luminous beam

1 Gibraltar Harbour Green Thick with fine particles

2 Two miles Clearer green Thick with very
from Gibraltar fine particles

3 Off Cabreta Point Bright green Still thick, but less so

4 Off Cabreta Point Black-indigo Much less thick, very pure

5 Off Tarifa Undecided Thicker than No. 4

6 Beyond Tarifa Cobalt-blue Much purer than No. 5

7 Twelve miles Yellow-green Very thick
from Cadiz

8 Cadiz Harbour Yellow-green Exceedingly thick

9 Fourteen miles Yellow-green Thick, but less so
from Cadiz

10 Fourteen miles Bright green Much less thick
from Cadiz

11 Between Capes Deep Indigo Very little matter,
St. Mary and Vincent very pure

12 Off the Burlings. Strong green Thick, with fine matter

13 Beyond the Burlings Indigo Very little matter, pure

14 Off Cape Finisterre Undecided Less pure

15 Bay of Biscay Black-indigo Very little matter,
very pure

16 Bay of Biscay Indigo Very fine matter.
Iridescent

17 Off Ushant Dark green A good deal of matter

18 Off St. Catherine's Yellow-green Exceedingly thick

19 Spithead Green Exceedingly thick

Here we have three specimens of water, described as green, a clearer
green, and bright green, taken in Gibraltar Harbour, at a point two
miles from the harbour, and off Cabreta Point. The home examination
showed the first to be thick with sus