SEA-FISHERIES LABORATORY. 331 



the two generally agreed closely. Although there does 

 not seem to be any connection between the plankton 

 catches and the daily variations in the actinometer, still 

 there does seem to be a relation between the marked rise 

 in all the plankton nets on April 13th and the permanent 

 increase in the amount of sunlight which set in a week 

 before. On April 5th the actinometer reading was 12'5 

 seconds, on April 6th it was 3'5, and from that time till 

 the end of the month it ranged only between 2 and 6 

 seconds, and the average for the week preceding the great 

 increase in plankton was 3*3 seconds, while for the week 

 previous to that (March 30th to April 5th) the average of 

 the actinometer readings was 9*9 seconds. The threefold 

 increase in the sunlight from 9*9 to 3*3 seconds was 

 followed after a week by an eight-fold increase of the 

 surface phyto-plankton (from about 100,000 to about 

 800,000 Diatoms per haul). This actinometer series of 

 observations tends to confirm the correspondence between 

 total hours of sunshine and the volume of the plankton 

 noted above. 



During this period the sea-temperature (surface) did 

 not vary much, the curve being a great contrast to that 

 of the sunshine. In the month from March 27th to 

 April 26th the temperature of the water rose only 1 degree 

 Centigrade, from 7'1° C. to 8*1° C. ; and during the four 

 days from April 5th to 9th, when the sunshine record 

 increased from 12'5 seconds to 2 seconds (by the actino- 

 meter), the sea-temperature increased only from 7*075° to 

 7*9° C, and the average of the five observations on these 

 days is 7'555° C. It is clear, then, that change in tempera- 

 ture will not account for the sudden increase in the 

 plankton which seems to have begun on April 9th or 10th 

 — after five days of increased sunshine. 



The present year seems to have shown an unusual 



