280 
Proceedings of the Boyal Society 
Percentage Composition of Soluble Portion . 
Na . 
. = 32*4 
Fe . 
. = 0-5 
nh 3 
. - 1*2 
Si0 2 
. - 1-2 
S0 4 
. = 41-3 
C0 2 
. - 12-3 
Cl . 
. = 8*8 
Organic matter 
. = 2-4 
Mg . 
• 
. = trace 
100-1 
From these results it will be seen that the portion of this sample 
soluble in water, which I suppose to he the reh proper, is mainly a 
mixture of sulphate of soda, carbonate of soda, and common salt, 
the sulphate being much the most abundant. I hope soon to have 
an opportunity of analysing some more samples of reh, the results 
of which analyses I shall communicate to the Society. 
4. On Spherical Harmonics. By Professor Tait. 
5. Proposed Theory of the Progressive Movement of Barometric 
Depressions. By Robert Tennent, F.M.S. 
This paper is a continuation and a fuller explanation of the pre- 
vious one, in which it was attempted to show why barometric de- 
pressions, or storms, move forward. In our present state of knowledge, 
exceptional cases in such an investigation are always to be found, and 
the subject is consequently taken up in a general point of view. 
It is attempted here to be shown, not how depressions always move, 
but how, under certain well-known circumstances, they may move. 
A depression of a small diameter was shown to be found under a 
comparatively high atmosphere, in which case it would tend to fill 
up. But when its diameter is great, say of several hundred miles, 
and underneath the same real atmospheric height, it may then be 
considered as existing under a comparatively low atmosphere, which 
