2o6 THE POPULAR SCIENCE MONTHLY. 



for usefully iiarticipating 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 endoAved with a 

 share of scientific insti-uction is testiHed 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 explor- 

 ers, to prepare themselves for doing so efiiciently, while they yet pos- 

 sess the vigor and physical powers that so much conduce to success 

 in such pursuits. 



DIAMOND-CUTTING.^ 



By De. 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-pow- 

 der, and one facet is polished at a time. Diamond-cutting proj^er 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 pi'actised 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 corre- 

 spond in exact proportions, and stand at fixed distances, so as to mul- 

 tiply the reflections and refractions, and produce the colors of the 



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



