BY i;. M. JOHNSTON, F.L..S. 33 



iuteiesting uccouut he states that he employed Messrs. 

 Negretti and Zambra's patent standard deep-sea ther- 

 mometers. The temperature was ascertained at tbe surface, 

 at 5 and 10 fathoms, and at a distance of 10 fathoms down 

 to the bottom. The Clyde sea area extends over 1,300 square 

 miles, and includes three grand plateaux, whose mean depths 

 were respectively 27 fathoms, 50 fathoms, and 80 fathoms. 

 The depth off Skate Island, near Tarbert, was as much as 

 107 fathoms. One of tbe most instructive investigations was 

 carried out at Strachur, in Upper Loch Fyue, where a depth 

 of 50 fathoms exists. 



In this region eight sets of observations were made with 

 the following results : — 



Surface. Bottom. 



Aprir20 



June 21 



Auiiust 11 ... 

 August 25 ... 

 September 27 

 November 17 

 December 29 

 Febrviary 4 ... 



The remarkable lesson to be derived from this investigation 

 is that the effects of the surface temperature in summer does 

 not penetrate to depth of 50 fathoms until the following Febru- 

 ary, and that even then, when at the maximum of bottom tem- 

 perature, itis lower than maximum surface temi:)erature by 8*2 '. 

 It is also instructive to observe that while the surface tempera- 

 ture ranges from 41'0 in December to 54'F in August, i.e., 

 total range of lo'l" ; the bottom temperature only ranges 

 between the extremes of 41 "9' in April, to 45*9^ in February, 

 i.e., a total range of 4'. Thus the bottom depths only feebly 

 follows at a wide interval the variations of the surface 

 temperature. 



Besides, it is clearly shown that in the hidden depths of 

 tbe sea there are hills, valleys, and protected basins, whose 

 temperatures varv with their depths, and with the physical 

 barriers which isolate basin from basin. When, therefore, 

 we realise that shallows bared at low tide were not even taken 

 into consideration, and when we have good reason for 

 assuming similar variation in the far-reaching Derwent sea 

 area of Tasmania, we have the strongest reasons against 

 resting upon any argument which assumes actual knowledge 

 of the temperature of its varying depths. 



At any rate these observations arc sufficient to cause us to 

 distrust theories based upon guesses or imperfect observation 



With res])ect to natural enemies, it is undoubted that in 



