“Royal Society. —* 389 
the water contains iron, is bitter, and clear, Common salt. 
abounds, and is collected by the inhabitants; but it is bitter, | 
and purgative to those unaccustomed to its use. Dr. Wollaston 
analysed the specimen which the author succeeded in chiseling 
from the block, which he found to be magnetic. In Dr. W’s 
analysis he found it to contain about 4 per cent. of nickel; the 
mineral is crystallized ; he dissolved it in nitric acid, added am- 
monia, and precipitated it with a triple prussiat. The specimen 
given to Dr. W. he found to be susceptible of magnetism, like all 
native iron ore ; he therefore confirms the author’s observations 
on the magnetism of the entire block, which does nat at present 
lie in the direction of its poles. 
May 23. A letter to the President from T. A. Knight, Esq. 
F.R.S. was read, containing his observations on ice found in the 
bottom of running water. Last February Mr. K. observed near 
his residence, that ice was attached to stones at the bottom of a 
river, while the surface was only covered with iniumerable spi- 
cula, but not converted into solid ice. He likewise found ice 
below water near a mill, where the water had been precipitated 
over stones : from the circumstance of the water having spicule 
running on its surface, and its temperature being quite as low 
as the freezing point, he is inclined to think that these spicula 
have been carried to the bottom by eddies and water-falls, and 
that coming in contact with certain stones somewhat cooler than 
the water, in this manner solid ice was formed at the bottom of 
rivers. If, however, ice has been found at the bottom of stag- 
nant water, he admitted that this theory would be inadequate to 
explain the phenomenon, Of the latter circumstance, indeed, 
he appeared to have no perfect knowledge. 
Sir Everard Home, Bart. furnished a curious paper on the for~ 
mation and use of fat in the tadpole. In his researches he was 
assisted by Mr. Hatchet, who analysed the eggs or ova of frogs, 
and discovered that they have no yolk. The tadpole of the Rang 
paradoxa is so large that its internal structure can easily be ex- 
amined, and it is sold in the market of Surinam for fish. Sir E. 
having obtained specimens of those tadpoles examined their 
anatomical characters, described the fins or fringes which serye 
as gills, noting the different appearances in their metamorphoses, 
the formation of the head of a perfect frog; and finally, the ex- 
tinction of the tail. The common tadpole, 1 it appears, lives on 
the gelatinous matter with which it is surrounded ; and to this 
end it is provided with a comparatively very long gut, which 
enables it to take up food; and that this gut is lined with fat, 
which in the animal’s progress from the tadpole to the frog gra- 
dually disappears; in 20 days it loses those fringes which served 
it forgills, and acquires a head and lungs; in seven more its tail 
Bb3 falls 
