shown, while in order to calculate the average values of vertical ex- 

 tinction coefficients for each class of colour of the sea, whole results of 

 measurements are used irrespective of the numbers of filters employed. 



Table 1 — The Vertical Extinction Coefficient for Every Class of Colour 

 OF Sea in Forell's Scale 



*Mean of 4 st. with equal transparency. 



tMean of 5 st. ^vith equal transparency". 



In the table the first column shows the colour of sea by Forell's scale. 

 The localities of observations are shown in the second column, the third 

 column shows the transparency of sea-water, which has been measured 

 by a white disk of about 30 cm. in diameter. The vertical extinction 

 coefficients are shown in the table from the fourth to eleventh columns, 

 the kinds of filters and the optical centers of response for each of them 

 are written at the heads of columns. The last column shows the date 

 of observations. 



Among the average values of vertical extinction coefficients in the 

 table some irregularities which cannot be negligible remain still. In 

 order to eliminate the irregularities the values of extinction coefficients 

 are plotted on a sheet taking the wave-length of light as an ordinate and 

 the value of vertical extinction coefficient as an abscissa. Considering 

 the relations between the vertical extinction coefficients for red (V-R3), 

 green (V-Gl), and violet (V-Vl), the points representing them are 

 connected smoothly for all classes of Forell's scale. Thus we get 



301 



