MARINE ALG OF BEAUFORT, N. C. 387 
of the test, and the fourth column giving the calculated percentage intensity of the 
light at the respective depths compared with full sunlight: 
Depth Length of | Equivalent] Relative 
EISEN) exposure. | standard. | intensity. 
Seconds. Seconds. Per cent. 
6 
Te) 28.0 46. 
60 23-0 38-3 
60 22.0 36.6 
60 9-0 15-0 
60 5-0 8.3 
120 7-0 5-8 
180 4:55 2-5 
240 2.8 1-2 
300 3-0 1-0 
The second record was made from 1:15 p. m. to 2:30 p. m., July 24, low tide 
on this day occurring at 2:15 p.m. The standards were made at 2 :30 p. m. of the 
same day and were exposed for 60, 45, 30, 25, 20, 15, 10, 5, and 3 seconds. The results 
were as follows: 
Depth Length of | Equivalent} Relative 
wees exposure. | standard. | intensity. 
Seconds. Seconds. Per cent. 
60 5 
60 17-5 
60 2 
120 3 
120 3: 
120 3 
» 
peeved 
MAMA A 
While these two records differ considerably, they agree in their main points and 
indicate several interesting conclusions: (1) A considerable portion of the light 
(nearly one-half) did not penetrate below the surface, probably because of the reflec- 
tion from the water and the suspended matter; (2) of the light which entered the water 
nearly one-half did not penetrate to a depth of 30 cm.; (3) at a slightly greater depth 
(1.2 m. at high tide, 60 cm. at low tide) the light was so reduced as to be almost lacking. 
These results are of great interest when considered in connection with the vertical 
distribution of the alge. While some of the difference in the records may be due to 
errors in the determinations, a considerable part is probably due to the fact that one 
was taken at high and the other at low tide. The water at high tide is notably clearer 
than that at low tide, and the record taken at high tide shows a correspondingly greater 
light intensity. 
These records, of course, show the effect of only the rays affecting solio paper, 
but it is these rays (toward the violet end of the spectrum) that are least absorbed 
by water. It is not known what proportion of the different rays penetrate water as 
turbid as that occurring here, or what is the intensity of the rays at the red end of the 
spectrum that reach the slight depths at which these measurements were made. There 
are evident errors in the methods used, but since the figures obtained could be, at best, 
only approximations, it did not seem worth while to give the time necessary to improv- 
ing the records. The figures given refer only to the water in the channel in front of 
the laboratory wharf. Efforts to obtain records from other localities far removed 
