252 Transactions. 



some degree upon the temperature of the tidal water, while that 

 of the river is wholly unaffected by it. It may perhaps be asked 

 why the mean annual temperature of the air in my observations 

 should be 52-5°, while in those of Mr Lewis it is only 47 "7°, and 

 the mean temperature of the water 48-5", as compared with 46°. 

 But this admits of an obvious explanation. For one thing, there 

 were uo observations taken by Mr Lewis in April, May, and the 

 greater part of June, while mine included these months, and 

 another thing to be taken into account is that my observations 

 were taken invariably about noon, when the heat of the day was 

 approaching its maximum, while those of Mr Lewis were taken at 

 all hours when the tide was up. 



I regret that I have not been able to procure a suflBciently 

 extended number of observations of the temperature of Lochrutton 

 Loch to be of much value, but by the kindness of Mr Beck and Mr 

 Lindsay I got observations made from the 8th to 19th August, 

 and from 13th September to 1st October, with the following 



results : 



Means. 

 Air. Wafer. Difference. 



From 8th to 19th August 58-3 61-1 +2-8 



,, 13th September to 1st October ... 54-3 55-2 +0-9 



From this we may probably infer that during at least the autumn 

 and winter months, and possibly in summer also, the temperature 

 of the Loch is, as a rule, in excess of that of the air. But the 

 observations are too limited in number to warrant any decided 

 conclusion being founded upon them. 



II. Seaweeds. By Mr Joseph Wilson (late Secretary). 



Seaweeds form by far the largest section of the Algse, which 

 is one of the three great classes into which the thallogenous plants 

 are divided. They are most abundant in the tropics, and many 

 thousand species have been found in the waters surrounding the 

 British Isles. These aquatic plants vary very much in size, form, 

 texture, and colour. Some species are entii'e and coi'iaceous, 

 others branched and filamentous ; some are flat, with or without a 

 midrib ; others are round, and in some instances measure several 

 hundred feet in length. One characteristic feature of all is that 

 they have no true roots, but absorb their food instead from the 

 medium in which they exist. 



