of the Fishery Board for Scotland. 



157 



examined by means of the hand-net ; but on the other four occasions 

 when the loch was visited the usual tow-net examination was made, 

 including temperature and other physical observations. 1 would here 

 acknowledge my indebtedness to Andrew Ralston, Esq., factor to Lord 

 Glamis, who not oidy allowed me the use of the boat for tow-netting the 

 loch, but also kindly sent one of the gamekeepers to assist me with the 

 work. 



Temperature and other Physical Observation*. 



The annexed Table contains a record of temperature and other 

 observations made at Forfar Loch on the different occasions when the 

 loch was examined by means of the tow-nets. 



Table showing Temperature and other Physical Observations. 



Date. 



Temperature. Wind. 



1 1 



Weather. ' 



Hour. 



1 Air. 



Surf. 



Water. 



Under 

 Surf. 



| 



Direction. 



Under 

 Surf, j 



Force. 



1897. 

 Nov. 3 



1898. 

 Mar. 4 



June 1G 



Sept. 15 



Degs. 

 Noon. 50-0 

 44-0 



72-2 



11 a.m. 59-5 



Degs. 

 47 5 

 36-8 

 62"2 

 59-5 



Degs. 

 21ft, 

 47-6 

 35ft. 

 37-0 

 35ift. 

 55-2 

 30ft. 

 59-0 



Degs. \ 

 .. S. E. 

 \ . j N. by E. 

 Easterly. 

 Calm. 



Light. 

 Mod'rate 

 Light. 



Sky overcast Slight ripple. 

 Sky cloudy. ; Not very rough. 

 Sky overcast Smooth. 

 Slight haze. Smooth. 



It will be observed that when the loch was examined in March the 

 temperature of the water was only about 5 degrees above freezing point. 

 It will also be noticed that the difference between the surface temperatures 

 in March and June was 25*4 degrees, and in March and September 22*7 

 degrees ; while the difference of the under-surface temperatures for the same 

 periods was 18*2 degrees and 22*0 degrees respectively. In the one case 

 there is a decrease, and in the other an increase, which is simply the 

 result of the surface and under-surface water having in the latter month 

 become of a more uniform temperature. It may be also further remarked 

 that while the temperature of the water in March is considerably below 

 what it was in November, it is on each of these occasions nearly uniform 

 for surface and under-surface. All these results agree very closely with 

 what was observed at Loch Lomond, and are probably to be explained in 

 the same way in which I have tried to account for the differences observed 

 in the temperature readings obtained in that loch. 



Pelagic Entomostraca Captured by the Tow-Nets. 



The free-swimming Entomostraca in Forfar Loch appear to consist 

 chiefly of three species, viz. : — Diaptomus gracilis, G. O. Sars ; Cyclops 

 strenuus, Fischer ; and Daphnia lacustris, G. O. Sars. A few other 

 species were captured in the tow-nets, but they were all of rare occurrence. 



Notwithstanding the great difference of 22 to 25 degrees Fahrenheit 

 between the summer and winter temperature of the water referred to in 

 previous remarks, the Daphnia were found to be abundant on ail lour 

 occasions when the loch was tow-netted, though they were apparently 

 more plentiful in June and September ; a few of the males of Daphnia 



