192 Troceedings of the Royal Society of Edinburgh. 



The following communications were read : — 



1. Observations on the Temperature and Hygrometric state 



of the Island of Barbadoes. By R. Lawson, Esq., As- 

 sistant-Surgeon of H. M. 47th Regiment. 



2. On the Growth and Migration of the Sea- Trout (Salmo 



Trutta). By Mr John Shaw, Drumlanrig. 

 The author has here pursued the same course of experimental 

 enquiry regarding the sea-trout, as that formerly followed in rela- 

 tion to the salmon. Having obtained impregnated ova, from a pair 

 of spawnhig fish, he conveyed these ova to his experimental ponds. 

 This was on 1st November 1839, and the young Avere excluded 

 from the ^g'g in 75 days. They resembled salmon of the same 

 age, but were somewhat smaller and paler. They took two years 

 to grow about seven inches, and the majority were then converted 

 into smolts. But about one-fourth did not assume the silvery lustre ; 

 and this peculiarity, Mr Shaw thinks, distinguishes a like proportion 

 even in the rivers. He then experimented on the smolts in the 

 natural streams, and found, that, after descending to the sea, they 

 returned as herlings (Salmo alhus of Dr Fleming) in July and 

 August, with an addition to their weight of seven or eight ounces. 

 These herlings spawn towards the end of the season of their first 

 ascent ; and, after revisiting the sea, they ascend the rivers again 

 in the ensuing months of May and June, with an average weight of 

 2J lb. This increase takes place almost entirely in the sea. After 

 spawning for the second time, they descend for the third time to 

 the sea, and make their appearance again in fresh water in the 

 course of the ensuing summer, weighing 4 lbs. They are now in 

 their fifth year, including the two^seasons they had passed as fry, 

 anterior to the assumption of the migratory dress and instinct. De- 

 scending seawards for the fourth time, they weigh about 6 lbs. when 

 next seen in the rivers, in the course of their sixth summer. These 

 at least were the progressive changes and ratio of increase ob- 

 served by Mr Shaw, in specimens distinctively marked, and care- 

 fully noted, when retaken in the river Nitli successively from year 

 to year. 'Ihe peculiar marks imposed each season are detailed in 

 his paper, and the whole subject is illustrated by an extensive series 

 of specimens, from the day of hatching, to the middle of the sixth 

 year. These specimens are now" in the Society's Museum. 



3. Experiments with Hydro- and Thermo-Electric Currents ; 



and an Examination of Metals long exposed to Thermo- 

 Electric Currents. By R. Adie, Esq. 



