166 On the Porosity of Agates, Calcedonies, &c. 
veyed between the tropics to replace those that have been re- 
moved, assume a movement towards the west. From this 
arises a circular progress towards the west, in the portion 
of it next the equator, and towards the east in its extra- 
tropical portion. 
Theory and observation point out to us five great circum- 
scribed currents or circuits, in the five great oceanic basins 
which reach the equator by one of their limits. 
2d, We may admit two other cireumpolar circuits, which 
surround, the one the north pole, the other the south pole, in 
their progress from the west to the east. 
3d, Independently of numerous consequences in relation to 
climates, the watering of the globe, the distribution of ther- 
mal lines on the earth, on the sea, &c., the excess of tem- 
perature in the northern hemisphere over the southern hemi- 
sphere results from the preponderance of the two northern 
circuits over the three southern circuits, a preponderance 
resulting from their more extensive surface, and the greater 
heat of their tropical waters, and lastly, from their greater 
extension in latitude. 
4th, Finally, it is evident, that on turning with a uniform 
movement a metallic vase warmed on one of its vertical 
faces, we may produce exactly the case of the masses of 
liquids in the sea, transported to different latitudes where 
the rotatory movement is different. We shall afterwards 
revert to the various consequences of this theory of the cur- 
rents of the sea, as well as to the experiment which ought to 
produce the principal results of it. These results, moreover, 
appear to us fully realised in nature, according to the laws 
followed by the currents marked out by M. Duperrey.* 
On the Porosity and Colouring of Agates, Calcedonies, §c. 
By M. NoGGnRATH. 
In the last century many experiments were made to colour 
agate, calcedony, carnelian, &c., by solutions of metals, &c., 
* From Comptes Rendus, t. xxviii., p. 749. 
