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THE POPULAR SCIENCE MONTHLY.

for usefully participating in the progress of science is now placed within the reach of every one. The lustre of that energy and self-devotion which characterize the better class of explorers will not be dimmed by joining to it an amount of scientific training which will enable them to bring away from distant regions enlarged conceptions of other matters besides mere distance and direction. How great is the value to science of the observations of travelers endowed with a share of scientific instruction is testified by the labors of many living naturalists. In our days this is especially true; and I appeal to all who desire to promote the progress of geographical science as explorers, to prepare themselves for doing so efficiently, while they yet possess the vigor and physical powers that so much conduce to success in such pursuits.

 

DIAMOND-CUTTING.[1]
By Dr. A. C. HAMLIN.

THE process of diamond-cutting is a very simple matter to those acquainted with the nature of the gem. To cut the facets, two stones are cemented on two sticks, and rubbed against each other until a facet is cut; then the position of one of the stones is changed, and another flat surface is cut. The process is thus continued until the gem is faceted all over. After the facets are cut, and a definite form given to the stone, the diamond is placed in the hands of the polisher, who fastens it in solder, and then holds it against a small steel disk revolving horizontally with a speed of 1,500 to 3,000 times a minute. This disk is moistened with oil mixed with diamond-powder, and one facet is polished at a time. Diamond-cutting proper is a rapid operation, but the polishing is slow and tedious. One cutter can generally furnish sufficient work for four or five polishers.

There are a number of forms adopted by the lapidaries for these gems, but the two principal ones are the brilliant and the rose. The former pattern, first practised in Europe in the seventeenth century, is by far the best adapted for calling forth the powers of the gem. The other form is of unknown antiquity, and has long been in use among the Hindoos. It affords the largest beams of light for the weight, but it lacks greatly in colored reflections when compared with the brilliant.

For the perfection of the rainbow-play of hues, it is essential that the facets of the superior and inferior parts of the stone should correspond in exact proportions, and stand at fixed distances, so as to multiply the reflections and refractions, and produce the colors of the

  1. From a work on "The Diamond," in the press of D. Appleton & Co.