A System of Crystallography,: With Its Application to Mineralogy

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Richard Griffin. and Thomas Tegg, London., 1841 - Crystallography - 489 pages
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Page 96 - Care must be taken to employ specimens of each of them nearly agreeing in form and size, and also as much as possible in the quality of their angles. From the resistance these bodies oppose to the file, and from the noise occasioned by their passing over it, we argue with perfect security upon their mutual relations in respect to hardness. The experiment is repeated with all the alterations thought necessary, till we may consider ourselves arrived at a fair estimate, which is at last expressed by...
Page xxvi - The same number of atoms combined in the same way produce the same crystalline form, and the same crystalline form is independent of the chemical nature of the atoms, and is determined only by their number and relative position.
Page xxiii - ... specific gravity fall between the fixed limits, and cannot exclude the individual from this order. The other parts of this character are now to be taken into consideration. If the appearance of the individual be metallic, its colour must be black, otherwise it cannot belong to the order Ore. But the appearance is not metallic ; therefore the colour of the individual is quite indifferent ; that is, this conditional characteristic mark does not affect the individual, and consequently cannot decide....
Page xxiii - ... particularly if the appearance be not metallic ; and a high degree of hardness. The observation of these will immediately decide whether an individual can belong to any particular class, order, genus, or species. It is understood, that if it be not thereby excluded, the other characters must next be examined, till either an excluding one be found, or if not, the individual may be considered as belonging to that class, order, &c., with which it has been compared and found to agree.
Page 3 - A rhomboid is that which has its opposite sides equal to one another, but all its sides are not equal, nor its angles right angles.
Page 124 - After remarking that the mathematician positively knows that the sum of the three angles of a triangle is equal to two right angles...
Page xxiv - ... concur. These properties agree consequently with the whole character of the order, as far as it is applicable to the individual, and determine it to belong to the order Ore, or, in shorter terms, to be an Ore. It will be advisable to beginners, who do not yet possess a sufficient practice in the use of the Characteristic, also to compare the characters of the remaining orders, which will enable them to find out any error they might have committed in the comparison of the individual with the characters...
Page 93 - MILLER'S account of these forms is this: — " The ' Holohedral Forms' of any system are those which possess the highest degree of symmetry of which the system admits. ' Hemihedral Forms ' are those which may be derived from a Holohedral Form, by supposing half of the faces of the latter omitted according to a certain law.
Page 15 - The following arcs are shown in the diagram : 42. The difference between an arc and a quadrant, is called the complement of that arc. The difference between an angle and a right angle is called the complement of that angle. — Thus, the arc Qe is the complement of the arc ec, and conversely cc is the complement of the arc eQ.
Page 96 - It is necessary also that the force applied in this experiment be always the least possible. "Every person, however little accustomed, will experience a very marked difference, if comparatively trying in this way any two subsequent members of the above scale, and thus the difference in their hardness will be easily perceived. A short practice is sufficient for rendering these perceptions more delicate and perfect so that in a short time it is possible to determine differences in the hardness very...

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