of the Fishery Board for Scotland. 



465 



This superiority is very clearly shown by a comparison of the informa- 

 tion given as to the state of matters near Smith Bank in the Moray 

 Firth in February last, by the two methods respectively. What is 

 the conclusion to be drawn from the observations of temperature and 

 specific gravity j duliuilud" in III . Surely that of almost perfect 



uniformity. These purely physical observations give no clear indica- 

 tion of the advance of the water along the bottom from the North 

 Sea into the Moray Firth, which was undoubtedly taking place at the 

 time. The temperature and the specific gravity of the surface, inter- 

 mediate, and bottom layers are almost identical. And yet at the time 

 those observations were made, the process of replacement of the one 

 kind of water by the other was actually in progress. Shortly before the 

 ' Jackal ' went to the Moray Firth a series of westerly and north-westerly 

 gales passed over the North of Scotland. The observations in the Pentland 

 Firth towards the end of January were impeded by the strong north- 

 westerly winds prevailing, and very unfortunately the weather in the 

 Moray Firth was such as to make it impossible to complete the whole of 

 the observations as originally planned. The results given in Table VII. 

 are however quite sufficient to exemplify the intermediate stage in the 

 replacement in the Moray Firth of the surface Atlantic water by the 

 bottom water of the North Sea. Without exception the samples of 

 water collected from the bottom give values for D higher than 1 *47 00, 

 and with one significant exception the surface waters give on the other 

 hand values for D lower than 1 -4600, that is to say, the water found at 

 the bottom of Moray Firth corresponded in chemical composition to the 

 samples collected during the cruise of the ' Jackal ' from the central portion 

 of the North Sea and also to the samples collected by Mr Grey in 

 northern latitudes, and on the other hand the chemical composition of 

 the surface samples was practically identical with the water found some 

 twelve days previously filling the whole area immediately to the north of 

 Scotland. The one exception is the surface water at Station I., but so 

 far from being in contradiction with the view above stated, it may be 

 said to prove the rule. When these results were first tabulated this 

 apparent discrepancy at once caught my attention. 



The fact that this sample was collected in the narrow channel between 

 the .Sutors, taken in conjunction with the fact that the other surface 

 sample collected at the same., spot gave a value for D in accordance with 

 all the other surface samples, led me to express the following opinion : — 

 If the view be correct that a value for D higher than 1-4700 is 

 characteristic of the North Sea water flowing in along the bottom, then 

 this particular sample must have been collected during flood tide when 

 the strong inflow through the narrow channel might easily bring the 

 water from lower layers to the surface, and further, the sample from the 

 same spot, which gave a value for D corresponding with all the other 

 surface samples, must have been collected at ebb tide. 



At the time I had nothing but a table giving the analytical results and 

 the number of the stations at which the different samples were collected. 

 When I looked up the observation books I found that the first sample had 

 been collected at 3J hours' flood and the second at 2A hours' ebb. 



The uniformity in the temperature from surface to bottom observed on 

 this occasion as occurring generally in the Moray Firth, may, I think, be 

 easily explained when it is remembered that the weather previous to the 

 commencement of the gales which brought about this interchange of waters 

 had been very cold, and that the layer of Atlantic water still found at the 

 surface when the samples were collected was so thin as to permit the lower 



