[Illustration: INGRAM'S ROTARY PERFECTING PRINTING-MACHINE.]
One of the most important machines in the Exposition, from the American point of view, is the "double Macarthy roller-gin," exhibited by Platt Brothers & Co. of Oldham, England. It is a curious instance of how machines sometimes revert to their original types. The oldest machine for ginning cotton is undoubtedly the roller-gin, and it was known in India, China and Malaysia long before Vasco da Gama turned the Cape of Good Hope and opened the trade of the East to the Portuguese and their successors. The common roller-gin of Southern Asia was shown at the Centennial from Hindostan, Java and China, and is exhibited here from Java. It has a pair of rollers about the size of broomsticks, close together and turning in different directions, which pinch and draw the fibre through, while the seeds are prevented from passing by the closeness of the rollers. Whitney's invention of the saw-gin in 1794 revolutionized the business and changed the whole domestic aspect of our Southern States. In it the fibre is picked from the seed by means of saw-teeth projecting through slits in the side of the chamber in which the seed-cotton is placed. But the roller-gin has again come upon the stage, and with the late improvements is likely to become the gin of the future. When the close of our civil war put an end to the "cotton famine," as it was called, in Europe, and American cotton resumed its place in the market, the export of the East Indian and Egyptian cottons would have been immediately suppressed if they had not possessed the roller-gin in those countries. Ten thousand of the double Macarthy gin are used in India, and five thousand of the single roller-gin in Egypt. It is understood that the saw-gin is used in but a single district in India. While the saw-gin injures any variety of cotton by cutting, tearing, napping and tangling the fibres, its action upon the long and fine staple called "sea island" is ruinous, and the roller-gin alone is suitable for working it. The slow action of the single roller-gin, cleaning about one hundred and fifty pounds of lint per day, made its cultivation too expensive, but the double roller-gin will clean nine hundred pounds in ten hours, or one hundred and twenty pounds an hour of the common upland short-staple cotton. It is thought by Southern members of the United States commission that the introduction of the double roller-gin into our country would greatly increase the profitableness of the culture of cotton, and especially of the "sea island," which is at present much neglected, and in the growth of which we need fear no rivalry. Each roller is made of walrus leather, and rotates in contact with a fixed knife, dragging by its rough surface the fibres of cotton between itself and the knife. A grating holds the seed-cotton. Besides these parts there are moving knives to which are attached a grid or series of fingers. At each elevation of the moving knives, the grids attached thereto lift the cotton to the elevation of the fixed knife-edge and of the exposed surface of the rollers: on the descent of each moving knife the seeds which have become separated from the fibre are disentangled by the prongs of the moving grid passing between those of the lower or fixed grid about seven hundred and fifty times per minute, and are by this rapidity of action flirted out.