364 



the salt adhering, derived from the sea, in which they grew. The 

 proportion of iodine, as indicated by testing the saline matter ob- 

 tained from the ash, varied in each. It was found very abundant in 

 tangle, with a trace of bromine, and especially in the stem. In the 

 ash of each also a notable proportion of phosphate of lime was found, 

 with more or less of carbonate of lime and magnesia. 



In conclusion, the author oifers some general remarks — 1st, On 

 the absence in these algse of starch, fatty or oily matter, and sac- 

 charine matter. 2d, On the necessity of minute research to deter- 

 mine the exact nature of their several proximate principles. Sd, 

 On the loss sustained by washing the weeds preparatory to their 

 being used as food, thereby diminishing their value. 4:th, On their 

 value as articles of food, if the nitrogen they afford may be consi- 

 dered as a criterion of their nutritive power : a table is given showing 

 the proportion of this substance in each, as determined by Professor 

 Apjohn, exhibiting the unexpected result, that these esculent algse 

 are actually richer in nitrogen than flour of the first quality, bth^ 

 On the advantage likely to be derived, especially by persons of the 

 labouring class, in regard to health, from their more general use. 

 6th, On their efficacy as manures, on account of the nitrogen which 

 they yield in the act of decomposition, and the inorganic compounds 

 they supply to the soil. Lastly, On the part they perform in the 

 economy of nature — in purifying sea-water by removing excess of 

 carbonic acid, and probably azote — and in separating and storing up, 

 not only most of the inorganic elements which exist in terrestrial 

 plants, but others, especially those powerful medicinal agents, iodine 

 and bromine, as if specially for the use of man. 



2. On the Deflection of the Plumb-Line at Arthur's Seat, and 

 on the Mean Density of the Earth. By Lieutenant-Colonel 

 James, R.E. Communicated by Professor Forbes. 



The author states that the results of the Trigonometrical Survey 

 of Great Britain are now nearly ready for publication, and that he 

 has deduced from them the most probable measures which they 

 afford of the length of a meridian, and the figure of the earth. 



After determining the most probable spheroid from all the astro- 

 nomical and geodetical operations in Great Britain, it has been found 

 that the plumb-line is sensibly deflected at several of the trigono- 



