April 17, 1885.] 



♦ KNOWLEDGE ♦ 



327 



PRODUCTIO.X 



OF IXDLA-iaUBER 

 BRAZIL. 



IN 



CONSUL ANDREWS, of Rio de Janeiro, says that 

 the rubber industry is the principal resource of the 

 two great prov-inces of the Amazon Valley, I'ara, and 

 Amazon, and its product occupies the third place in the 

 list of the national exports. The rubber tree requires a 

 growth of twenty to twenty-five years before it begins to 

 produce, and tor this reason little or nothing has been done 

 for its propagation. The milky sap which forms the 

 rubber is taken from the wild tree which is to be found 

 tliroughout the forests of the Amazon, and many of its 

 affluents. The industry, being jirincipally in the hands of 

 an uneducated and half-civilised nomad population of 

 Indian mixture, is of a crude character, and is pursued 

 mostly on the national domain. Nothing of late years has 

 been done to improve the system of labour, and a wasteful 

 and exhaustive system has been followed for half a century, 

 with the result that millions of india-rubber trees have 

 been destroyed, and many others abandoned from pre- 

 mature and e.xcessive use. There are iustances of groves 

 of trees which, by careful use, and by not permitting them 

 to be tapped in the months of August and September, in 

 which they change their leaves, have been yielding for 

 thirty years, and are still in good producing condition. The 

 tree thrives only on soil which is annually submerged to a 

 depth of three or four feet, and prefers tlie lowest and most 

 recent river deposit. The rubber gatherers are temporary 

 squatters, and their usual dwelling is a hut with low roof 

 of psilms, beneath one end of which there is a raised floor, 

 or framework of lath, one or two yards from the ground, 

 to which the occupants retreat at high water. The 

 following is the system employed in collecting the india- 

 rubber. Narrow paths lead from the gatherer's hut 

 through dense underwood to each separate tree, and 

 when the dry season sets in small holes are cut with a 

 hatchet in the bark of the trees. The milk-white sap imme- 

 diately begins to exude into pieces of bamboo, tied below 

 into little clay cups, set under the gashes to prevent its 

 trickling down the stem. The gatherer goes from tree to 

 tree, and, on his return visit, he pours the contents of the 

 bamboos into a large earthern vessel, piovided with straps, 

 which he empties at home into a large turtle-shell. He 

 then commences to coagulate it with the smoke of palm- 

 nuts, and pours a little of the milk evenly on a light 

 wooden shovel, which he thrusts into the thick smoke 

 issuing from a little narrow chimney made by the 

 neck of an earthern bottle. He moves the shovel several 

 times to and fro with great rapidity, when the milk 

 is seen to consolidate and to take a greyish-yellow 

 tinge. He then puts layer on layer, until at last 

 the rubber on both sides has reached a thickness of 

 two or three centimetres ; it is then cut on one side, taken 

 off the shovel, and hung in the sun to dry. A good work- 

 man can prepare five or six pounds of solid rubber in an 

 hour. From its initial colour of clear silver-grey it turns 

 to a yellow, and finally becomes the well-known dark 

 brown of the rubber, such as it is exported. The more 

 uniform, the denser, and freer of bubbles the whole mass 

 is found to be, the higher the price it realises. Almost 

 double the value is obtained for the first-rate article over 

 that of the most inferior quality, which is nothing but the 

 drops collected at the foot of the trees. The export of 

 india-rubber has increased rapidly in the past few years. 

 From Paril and Manaos, the two principal ports in the 

 Amazon Valley, the export during the five years from 

 1839—1844 was 2,-520,000 lb., of the value of £79,000. In 



the five years, 1854— 1859, it had increased to 21,500,0001b., 

 of the value of .£800,000; and in the five vear.s 1871—1879, 

 to GG,000,000 11)., of the value of .£l,i00,O00. In 1882 

 the quantity exported was about 22, 100,000 lb., with a 

 value of £3,000,000. A very heavy export duty is col- 

 lected on this article, the Imperial duty being 9 per cent, 

 on the value, and in addition a tax ot 12 per cent, is col- 

 lected by the province of Amazon, and 13 per cent by the 

 province of Para, making 22 per cent, on all that is 

 exported from the latter province, and 21 per cent, on 

 exj)orts from the former. — Journal of the Sociflij of Arts. 



CRITICAL METHODS OF DKTECTINC 

 ERRORS IN PLANE SURFACES. 



By Joun a. Bkasiiear. 



[A paper read before tbo Enj^ineers' Society of Western Peun- 

 Bylvauia, Dec. IG, 188-1.] 



IN our study of the exact methods of measurement in 

 use to-day, in the various branches of scientific inves- 

 tigation, we should not forget that it has been a plant of 

 very slow growth, and it is interesting indeed to glance 

 along the iiathway of the past to see how step by step our 

 Micron of today has been evolved from the cubit, the 

 hands-breadth, the span, and, if you please, the barleycorn 

 of our schoolboy days. It would also be a pleasant task to 

 investigate the properties of the gnomon of the Chinese, 

 Egyptians, and Peruvians, the scarphie of Eratosthenes, 

 the astrolobe of Hipparchus, the parallactic rules of 

 Ptolemy, Regimoutanus Purbach and Walther, the sex- 

 tants and quadrants of Tycho Brahe, and the modifications 

 of these various instruments, the invention and use of 

 which, from century to century, bringing us at last to the 

 telescopic age, or the days of Lip|iershay, Jannsen and 

 Galileo. It would also be a moat pleasant task to 

 follow the evolution of our subject in the new era 

 of investigation ushered in by the invention of that 

 marvellous instrument the telescope, followed closely 

 by the work of Kepler, Scheiner, Oassini, Iluyghens, 

 Newton, Digges, Nonius, Vernier, Hall, DoUond, Herschel, 

 Short, Bird, Ramsden, Troughton, Smeaton, Frauen- 

 hoffer, and a host of others, each of whom has con- 

 tributed a noble share in the elimination of sources of 

 error, until to-day we are satisfied only with units of 

 measurements of the most exact and refined nature. 

 Although it would be pleasant to review the work of these 

 past masters, it is beyond the scope of the present paper, 

 and even now I can only hope to call your attention to one 

 j)hase of this importiint subject. For a number of years I 

 have been practically interested in the subject of the pro- 

 duction of plane and curved surfaces, particularly for optical 

 purposes — i.e., in the production of such surfaces, free, if 

 |jossil)le, from all traces of error, and it will be pleasant to 

 me if I shall be able to add to the interest of this associa- 

 tion by giving you some of my own practical experience, 

 and may I trust that it will be an incentive to all engaged 

 in kindred work to do thai work vxll. In the production of 

 a perfectly plane surface, there are many diliiculties to con- 

 tend with, and it will not be possible in the limits of this 

 paper to discu.ss the methods of eliminating errors when 

 found, but I must content myself with giving a description 

 of various methods of detecting existing errors in the 

 surfaces that are being worked, whether, for instance, it be 

 an error of concavity, convexity, periodic or local error. A 

 very excellent method was devised by the celebrated Ross, 

 which is frequently used at the present time, and those 



