417 



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

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

 their fifth year, incUiding 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 G 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 Nith successively from year 

 to year. The 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 hatchmg, 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. Communicated 

 by Dr Traill. 



The author commences his paper with a description of two 

 forms of Electric Batteries, which he used in bis experiments, and 

 which consisted of bars of antimony and bismuth. One of these, 

 which was chiefly intended for currents excited by solar and astral 

 influences, was so delicate as to make the needle of the galvano- 

 meter deflect at right angles, when one end of the battery was ex- 

 posed to the influence of clear summer's sun ; and he therefore 

 considers it a very delicate meteorological instrument. The other 

 form of battery was principally used for thermo-electric currents, 

 from a low flame of gas, or a spirit-lamp. 



With the former instrument he succeeded in decomposing cyanide 

 of silver, by exposure to the air for three months in winter, even 

 although the voltameter, in connection with the battery, was often 

 exposed to frost. 



In using the second form of instrument, he remarked, that water 

 is decomposed by copper poles, but not by poles of platinum, — a 

 fact, which appears to him to account for Professor Daniell not 

 having been able to produce electrolysis by primary thermo-currents. 

 He farther observed, that metallic salts yield readily to a thermo- 

 current, when the poles consist of the metal whose oxide forms the 

 base of the salt. 



On examining the effect of long-continued electrolysis on the 



