Intelligence and Miscellaneous Articles. 479 
reflecting two beams—one normally polarized in the plane of in- 
cidence, and the other polarized in a plane perpendicular to it, 
The chromatic properties exhibited by the picrates of ammonia 
and potash are very remarkable in their variety. Their crystals 
possess :— 
Ist. The well-known play of red and green light. If a little very 
dilute solution of pure picrate of potash be spontaneously evaporated 
in a hemispherical porcelain basin, so as to form a network of ex- 
tremely slender needles, and these be viewed by gas-light, the play 
of colours is singularly brilliant. 
2nd. Dichroism. When by spontaneous evaporation of large quan- 
_ titres of solution of potash, or, better, of ammonia salt, transparent 
prisms of =); to ;4 inch diameter are obtained; these, viewed witha 
doubly refracting prism by transmitted light, give two images—one 
pale straw-colour, and the other deep brownish red. 
3rd. The above-described property of catachroism, or reflexion in 
the plane of incidence of oppositely polarized beams.—Silliman’s 
American Journal, November 1860. 
EXPERIMENTS ON THE POSSIBILITY OF A CAPILLARY INFILTRA- 
TION THROUGH POROUS SUBSTANCES, NOTWITHSTANDING A 
STRONG COUNTERPRESSURE OF VAPOUR. POSSIBLE APPLICA- 
TION TO GEOLOGICAL PHENOMENA. BY M. DAUBREE. 
In the grand phenomena which are to us the principal manifesta- 
tions of the activity of the interior of the globe, we see every day 
enormous quantities of water disengaged as steam from great depths. 
It may be asked if these incessant losses are not partially at least 
made up by a supply from this surface; and if so, in what way are 
these infiltrations effected ? 
It would be difficult to imagine that this supply was produced by a 
free circulation; for the way open for a descent would at the same 
time form an outlet also for the escape of vapour; and this objection 
would apply more especially to the volcanic regions, where the in- 
ternal vapour has sufficient tension to send columns of lava with a 
density two or three times that of water, to great heights above the 
level of thesea. In trying to reconcile these apparent contradictions, 
I have been led to inquire if water could not reach the deep and 
heated reservoirs, which yield it in a variety of ways, not by means 
of extended fissures, as has hitherto been supposed, but also by the 
porosity and capillarity of rocks. 
M. Jamin’s ingenious experiments* have shown how considerable 
is the influence which capillarity exerts in changing the conditions 
of equilibrium, established through the intervention of a liquid 
column, between two opposite pressures. 
But in previous experiments the temperature was the same in all 
parts of the capillary tube. It appeared important, more especially 
in reference to the geological problemewhich I have indicated, to see 
what would happen if the temperature was much higher at one part of 
* Phil. Mag. vol. xix. p. 204, 
