386 BULLETIN OF THE BUREAU OF FISHERIES. 
Since the only photometer available to the author at that time was one intended 
for use in the air, this form was employed, being adapted as follows: All exposures were 
made with the photometer placed in a glass preserve jar of sufficient diameter to permit 
the photometer to lie flat on the bottom. The photometer was held in place by paper 
packed into the jar, care being taken that the slot for exposing the solio paper was not 
shaded by the packing. Ina dim room the slot was opened, the photometer was placed 
in the jar and securely packed, and the jar was tightly wrapped in black cloth. This 
was then taken to the desired situation, the jar being held horizontally with the slot 
directly on top, the cloth was quickly removed for the desired number of seconds and 
then quickly replaced, and the jar was then brought back into the laboratory. All 
changes in the apparatus were made in a dim room at a considerable distance from any 
window. The standards were obtained in this way by exposing the photometer within 
the glass jar to direct sunlight on an upper, unshaded, southern porch. 
For exposing the photometer below the surface of the water a shallow box, open at 
the top and of the proper size to hold the jar horizontally, was built, the sides of the box 
being just high enough to hold the jar in place and not shading the upper part of it. 
This box was then fastened to a handle marked with the desired distances. In a dim 
room the jar containing the opened photometer was placed horizontally in this box with 
the slot directly on top, and the box was tightly wrapped with black cloth. This was 
carried in a boat to the desired locality and held at arm’s length below the water, the black 
cloth was then removed, and the jar immediately sunk to the desired depth and held at 
that level for a definite time. The jar was then quickly brought within reach and imme- 
diately covered with the black cloth, not more than a second being required for this 
manipulation. The apparatus was then carried to the laboratory, where all changes 
of the photometer were made in a dim room. 
While the jar undoubtedly diminished the light reaching the photometer, this 
decrease would be the same in the standards and the tests. The effects of the light in 
these two cases may, therefore, be directly compared. 
Two records, one at high and one at low tide, were obtained in this way in the 
channel in front of the laboratory wharf in July, 1907. In the first of these the 
standards were made from 1:15 p. m. to 2 p. m., July 17, and the measurements 
below the water were made from 1 : 15 p. m. to 4 p. m., July 18, high tide on this day 
occurring at 2 p.m. In some cases, where the color of the test did not exactly match 
that of any standard, the time of the standard having an effect equivalent to that of 
the test was obtained by interpolating between the two standards showing the colors 
nearest to that of the test. Standards were made by exposing to direct sunlight as 
described above for 60, 30, 25, 22, 20, 15, 10, 5, 3, 2, and 1 second. ‘The results were 
as follows, the first column giving the depth below the surface at which the test was 
exposed, the second column giving the time of the exposure of the test, the third 
column giving the time of exposure of the standard having a color equivalent to that 
