Excerpt: ...This list must be taken as approximate, since in many instances the test has been made on one stone only, without possibility of obtaining an average; and as stones vary considerably, the figures may be raised or lowered slightly, or perhaps even changed in class, because in some stones the least stain or impurity may cause the heat effects to be altered greatly in their Pg 54 character, and even to become singly or doubly refracting, opaque or transparent, to heat-rays, according to the nature of the impurity or to some slight change in the crystalline structure, and so on. Selection of Singly refracting stones.Indexes of Rays of Light. Heat. Fluorspar1.4364.10varies Opal1.4792.10" Spinel1.7261.00 Almandine1.7641.00 Diamond2.4316.11double Selection of Doubly refracting stones.Indexes of Rays of Light.Heat. Quartz1.5454.7single and double Beryl1.5751.0varies considerably Topaz1.6354.1 " " Chrysoberyl1.7651.1 " " Ruby1.9495.1single and double The tourmaline has a light-refractive index of 1.63, with a heat index of none, being to heat-rays completely opaque. The refractive index of gypsum is 1.54, but heat none, being opaque. The refractive index of amber is 1.51, but heat none, being opaque. In some of the specimens the gypsum showed a heat-penetration index of 0.001, and amber of 0.056, but mostly not within the third point. In all cases the heat-penetration and refraction were shown by electric recorders. These figures are the average of those obtained from tests made in some cases on several stones of the same kind, and also on isolated specimens. Not only Pg 55 does the power of the stone to conduct heat vary in different stones of the same kind or variety, as already explained, but there is seen a remarkable difference in value, according to the spot on which the heat is applied, so that on one stone there is often seen a conductivity varying between 0.15 to 4.70. This is owing to the differences of expansion due to the temporary disturbance...

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Product Description: This scarce antiquarian book is a facsimile reprint of the original. Due to its age, it may contain imperfections such as marks, notations, marginalia and flawed pages. Because we believe this work is culturally important, we have made it available as part of our commitment for protecting, preserving, and promoting the world's literature in affordable, high quality, modern editions that are true to the original work...read more