676 
BULLETIN OF THE BUREAU OF FISHERIES 
I know of no direct measurements of the depth to which the infra red rays do 
actually carry heat into the sea water in measurable amount under the conditions 
of turbidity actually existing at sea, but even distilled water is so nearly opaque to 
them that they are almost entirely absorbed (for practical purposes, entirely so) in 
one meter, and their penetration into the sea is certainly less. That is to say, nearly 
half of the sun’s direct radiant heat is expended, theoretically, upon this thin surface 
film. 
According to a calculation carried out in the physical laboratory of Harvard 
University through the kindness of Prof. Theodore Lyman, 58 per cent of the energy 
conveyed by the visible part of the solar spectrum would be absorbed by passage 
through 9 meters more (i. e., a total of 10 meters) of perfectly clear distilled water, 
so that only about 20 per cent of the total solar energy entering the water would 
penetrate as deep as 10 meters, this small residual lying chiefly in the blue-green 
part of the spectrum. Certainly less than 1 per cent could penetrate as deep as 200 
meters — chiefly in the ultra violet. Probably this calculation would apply equally 
to pure salt water. The sea, however, is never clear; and in boreal coastwise waters 
such as the Gulf of Maine, which are always comparatively turbid, the fine particles 
in suspension — silt or plankton — absorb so much of the sun’s rays that the penetra- 
tion of heat is much reduced. 
It is, of course, with the depth to which the water of the gulf is measurably 
warmed by the direct penetration of solar radiation under conditions actually pre- 
vailing there that we are now concerned. This may be approximated by experi- 
ments that have been made in other seas. In the comparatively clear water of the 
Mediterranean, off Monaco, Grein’s (1913) measurements 55 of the penetration of 
different parts of the solar spectrum showed that the wave lengths as long as the 
blue-green, and longer, were virtually all absorbed in the upper 50 meters, red-yellow 
in the upper 10 meters, as appears in the following table condensed from his 
account. 
Intensity of light penetrating to different depths, taking the amount at 1 meter as 100 
Color and wave length 
Depth, meters 
Red, 
680-610 
Orange- 
vellow, 
620-585 
Green, 
570-486 
Blue-green, 
515-486 
Blue, 
476-420 
Blue-violet, 
435-400 
1 
100. 00000 
. 27000 
. 00021 
100. 0000 
.2000 
.0032 
.0001 
100. 0000 
16. 6000 
.2200 
.0030 
.0004 
100. 0000 
16. 6000 
.2500 
.0033 
.0010 
100. 000 
43. 700 
20. 100 
.550 
.004 
100.0 
80.0 
20.0 
1.0 
.1 
10 
50. 
100 ^ . 
200 
Translated into terms of solar energy, this means that at least 70 per cent of all 
the radiant solar heat that penetrated as deep as 1 meter was absorbed at a depth of 
10 meters; and as nearly all of the energy of the infra red certainly was absorbed in 
that upper meter of water, it is not likely that more than 13 per cent of the solar 
heat that entered the water at all reached as deep as 10 meters by direct radiation, 
“These experiments were made with a “revolving photometer,” for description of which, and of the method by which the 
degree of blackening of the photographic plates was measured, see Grein (1913). 
