SCIENTIFIC SUMMARY. 
103 
detritus , which, however, were only little developed in those parts which I 
visited. All islands consisting of the above rocks are characterised by the 
absence of grass-heaths, and are covered with forests from the bottom to the 
top. The four principal aspects of vegetation in these islands are — 1, man- 
grove swamps ; 2, beach forests ; 3, tropical forests, which fall under three 
groups, those growing on polycistine clay, those on calcareous or coralline 
strata, and those growing on plutonic formations ; 4, grass-heaths. 
CHEMISTRY. 
The Composition of the Water of the Nile. — Mr. J. A. Wanklyn has pub- 
lished an interesting note in the u Chemical News” (Oct. 29, 1875) on the 
subject of Nile water and its varying composition. Of course our readers- 
are aware that the Nile rises steadily to a vast height, reaching its highest 
level about the middle of September, and being lowest at about Christmas.. 
The cause of the rise of the river is said to be heavy rains in the months 
of April and May, the effect of this rainfall requiring the lapse of a consider- 
able time in order to exert its full influence. Possibly, too, the melting: 
of snow on mountains near the sources of the river may concur in; 
flooding the river. The height to which the Nile rises, as well as the exact 
period of the rise, varies from year to year, but it maybe stated broadly that 
from the end of May until Christmas the Nile is more or less in flood, and 
from Christmas to the end of May the Nile is low. The following is a 
tabular statement of the composition of the water in the different months : — 
Water of the Nile. 
Grains per Gallon. 
Date of Sample. 
1874 June 8 
Solids. 
. 15-0 
Chlorine. 
1-80 
Hardness. 
7-0 
July 
19 
. 13-0 
0-90 
6‘0' 
Aug. 
12 
. 120 
0-30 
8-5' 
Sept. 
20 
. 10-0 
0-40 
8-Qv 
Oct. 
12 
. 11-0 
0-40 
7-5' 
Nov. 
12 
. 12-0 
0-50 
8-0’ 
Dec. 
12 
. 9*0 
0-45 
6-5. 
1875 
April 
. 16-0 
1-00 
8-0 
May 
13 
. 22-0 
1*20 
10-0 
The remarkable point brought out in this table is the great relative alter- 
ation in the proportion of chlorine, that whereas in the beginning of June, 
just at the beginning of the rise of the Nile, the chlorine amounts to 1*8 
grain per gallon the chlorine sinks to 0-3 grain per gallon when the Nile 
has attained a great size, and remains at very little above that proportion 
until the end of the year. 
The Quantity of Tannin in Tea. — This question has been, with many 
others in relation to the chemistry of this plant, gone into by Mr. T. 
Wigner, whose papers have been published in the u Chemical News.” The 
number of the “ C. N. ” for Nov. 12, 1875, contains the author’s remarks 
