136                           PRECIOUS STONES.
	on The Therapeutics of Mineral Springs, 1904, " the idea of absorption of mineral substances through the skin has been negatived by repeated experimental observation. It is therefore incorrect to suppose that the outward action of Mineral waters can be in any way dependent on the absorption of their constituents through the skin ; for, it has been proved that the sound, and healthy human skin is not permeable to water, or to the fixed substances dissolved in it; even after prolonged immersion. Nevertheless it is asserted by some authorities that the skin has been found permeable to water, and watery solutions, when applied thereto in fine spray (at an elevated temperature) ; and it is suggested that the force with which this spray is thrown upon, and against the skin, serves to influence such absorption. Moreover, it may be borne in mind that volatile, or gaseous constituents of mineral baths can be absorbed through the respiratory organs; indeed, too, it seems probable from experimental observation, that the skin itself is permeable to certain volatile, and gaseous constituents of baths; as, for instance, carbonic acid gas, and sulphuretted hydrogen." Some writers have said that the Emerald should be worn on a Friday for good luck, because dedicated to Venus, the Goddess of that week-day. But a mis­taken notion underlies this practice, considering that the Scandinavian Venus, Freya, is here signified, the wife of Odin, and a woman of bad character. Never­theless, to regard Friday as of ill omen for then under­taking anything of importance, is only a relic of an old Puritan superstition. It is simply a fortuitous circum­stance that various untoward events have occurred on a Friday. Charles Dickens always chose this day of