244 
ground, and of the red upon the white ground. The vibrations 
of the energy as in the case of a ray of polarized light are 
iransverse to the wave length. 
Direction oF THE Hat VIBRATIONS IN PoRPHYRITE 
IV. PHYSICAL OBSERVATIONS— 
The physical constitution of granites involves something 
in addition to a knowledge of their intimate structure and 
origin—it would lead naturally to a fuller and more precise 
inquiry, and of course, information, as to such rocks and their 
capacities—(1) in presence of water. (2) in presence of fire. 
1. The conclusion after a course of patient research 
undertaken by the late Prof. Ansted, was that, in regard to the 
former element, granite generally contains about 0:8 per cent. 
of water, and is still capable of absorbing about one-fourth 
more, or 0°2 per cent. So that a cubic yard of granite of two 
tons in weight contains in its ordinary state about 3°5 gallons 
of water, and some specimens can absorb nearly a gallon more, 
on being placed in pure water for a short period. An accurate 
and painstaking worker, M. Daubrée, member of l’Academie 
des Sciences, Paris, relates that water is found and stored up 
in the interstices, fissures, and cavities of the crust of the 
globe—but further it exists in a perfectly invisible state locked 
up in the actual substance of the rocks. All rocks, even the 
most compact, granite and quartz, enclose it in their pores, 
although from their extreme fineness quite outside the reach of 
magnifying power, it is retained by capillary attraction, and is 
in no wise apparent. But dessication, in consequence of which 
it is driven out, causes the rock to lose a sensible fraction of its 
weight, at the least, some ten thousandths. 
