278 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



during the periodic cruises is determined by a Richter 

 thermometer. The deep temperatures are observed by a 

 Nansen deep-sea thermometer, used in the small Nansen- 

 Pettersson insulating water-bottle. In the cruises after 

 September of this year an Ekman water-bottle and 

 Richter reversing thermometer were used, the other 

 instrument being under 1 repair. 



It will be shown later that the sea-temperatures at 

 Hydrographic Stations 5, 6, and 7, are probably of con- 

 siderable importance, and it is advisable to discuss them 

 in some detail, endeavouring to ascertain how far the 

 individual temperatures observed on each cruise express 

 relatively stable conditions, or are only " accidental " 

 variations. It is necessary to consider (1) the effect of 

 the variability in date of the periodic cruises ; (2) the 

 variation in surface temperature along the line of stations 

 between Holyhead and Calf of Man ; and (3) the varia- 

 tion of the sea-temperature with the depth. 



(1) It is clearly impossible so to arrange matters 

 that the periodic cruises are always made at the same 

 dates in each year. The February cruise has been made 

 as early as 27th January, and as late as 25th February, 

 and the dates of the other quarterly cruises have also been 

 inconstant (Table V.). Strictly speaking, it is impossible 

 to compare the results of different years without making 

 allowance for this variability, since the difference of 

 temperature which might have taken place between (say) 

 the 27th of January and the 25th of February, might be 

 greater, or nearly as great as the differences between the 

 temperatures of successive years. 



It is necessary, then, to " correct" these data: to 

 reduce them to the data which would have been obtained 

 if the cruises had been made on the same days in each 

 year. This might be done by interpolating from an 



