328 
M. Humboldt’s Observations on the Horary 
of transparent, laminar, carbonate of lime, which divides the mass 
into small prisms ; sometimes it is coaly matter, and at other 
times they are enveloped with a crust of compact sulphuret of 
iron. In the centre is a nucleus of a pale-yellow or grey colour, 
compact, fine granular, having the appearance of brown flint, 
and traversed by impressions of gramineae : it is this nucleus 
which contains the phosphate of lime. I have found in a spe- 
cimen, the specific gravity of which was 2.65, 
Lime, - 
- 
0.469 
Phosphoric Acid, 
- 
0.39 1 
Protoxide of Iron, 
- 
0.072 
Carbonic Acid, 
- 
0.045 
Alumina, 
- 
0.006 
Coal, Water, and loss, 
- 
0.014 
Phosphate of Lime, - 
- 
0.863 
Carbonate of Iron, 
- 
0.117 
Alumina, - 
- 
0.006 
Coal, Water, and loss, 
- 
0.014 
“ But the relative proportion of phosphate of lime and car- 
bonate of iron varies much. The crust of a nodule assayed in 
a covered crucible, without addition, gave 0.20 of hard cast-iron 
( de fonte dure), equivalent to 0.43 of carbonate of iron, and a 
slag weighing 0.56, which was opaque, of an apple-green colour, 
and entirely similar to melted phosphate of lime. 1 ’ — Annates des 
Mines 1825. 
Art. XVII. — Observations made for Determining the Progress 
of the Horary Variations of the Barometer under the Tropics , 
from the Level of the Sea to the Ridge of the Cordillera of the 
Andes. By M. de Humboldt. 
M © de Humboldt, in the volume of his Travels lately pub- 
lished in Paris, states the following interesting conclusions re- 
garding the horary variations of the barometer under the Tropics. 
1st, The horary variations of the barometer are perceptible 
in all parts of the earth, and to the height of 2000 toises. They 
are periodical, and consist of two ascending motions and two de- 
scending motions, which are performed in the interval of a day. 
The periods of the maxima and minima are not equidistant ; 
they present separations of two hours. The maximum of the 
morning falls between 8J hours and 10§ ; the minimum of the 
afternoon, between 3 hours and 5 ; the maximum of the evening, 
between 9 hours and 11 ; and the minimum of the night, be- 
tween 3 hours and 5. 
