72 ANNUAL OF SCIENTIFIC DISCOVERY. 



rollers many hundred per cent., nncl, what is of far greater importance, 

 mule practicable an infinite number of intricate engraving which could 

 never have been produced by hand labor applied directly to the roller. 



A further improvement was made by tracing with a diamond en the 

 copper roller, covered with varnish, the most complicated pattern?, by 

 means of eccentrics, and then etching. 



The combination of mill engraving with the tracing and etching precedes 

 naturally followed, adding immensely to the resources of the engraver and 

 printer in the production of novel designs. 



Another development of this art is the tracing of patterns on the surface 

 of rollers, which has been effected by machines constructed on the principle 

 of the pentagraph. Although this invention dates from 1834, still it is only 

 of late years that it has been successfully applied. 



But if mechanical art has greatly assisted the engraver, chemistry has 

 rendered him equally important services, by enabling him to abandon costly 

 and cumbrous modes of impressing by force the designs on the cylinder, 

 substituting for them a great number of etching processes. By some of these 

 processes, as by every other addition to the resources of the engraver, an 

 entirely new and beautiful class of engraving is produced, unattainable by 

 any other known means. 



A very recent improvement is highly interesting in a scientific point of 

 view. It is the application of galvanism to the diamond tracer. By com- 

 bining the galvanic action with the eccentric motion, most beautiful and 

 delicate engravings can be produced. This is effected by tracing the pat- 

 tern with a varnish on a zinc cylinder, which is so placed in the engraving 

 machine that, as a needle passes over its surface, and comes in contact with 

 the zinc, the galvanic current is established, and, by simple machinery, causes 

 the diamond to trace the corresponding pattern on the copper roller. The- 

 communication is so rapid and so precise, that this invention of Sir. Gaiffe, 

 of Paris, bids fair to produce very important results. Galvanism is also 

 made use of for producing effects on roller surfaces by depositing copper 

 thereon. 



To give an idea of the extraordinary influence which the introduction of 

 machinery and improvements in engraving have had in cheapening the cost 

 of printed calicoes, I may state that large furniture patterns, such as arc 

 required for Turkish, Egyptian, and Persian markets, into which sixteen. 

 colors and shades enter, would have cost formerly from thirty to thirty-live 

 shillings per piece, because they would have required sixteen distinct appli- 

 cations of as many different blocks, and would have occupied more than a 

 week in printing, where the same piece can now be printed in one single 

 operation, which takes three minutes, and costs five or six shillings. So 

 rapid is the progress of one branch of manufacture in connection with 

 another, that it has only recently been possible to produce the rollers capa- 

 ble of performing this operation, that is to say, cylinders of copper forty- 

 three inches in circumference by forty-four inches long. For light styles of 

 printing, the time required to print a piece of thirty-six yards is not more 

 than one minute. 



Chemistry. But the discovery which has exercised more influence than 

 any other on the progress of calico printing is the application of chlorine 

 gas as a bleach in- agent. Previously to the employment of this gas (chiefly 

 as bleaching powder), the imperfect bleaching of a piece of calico required 

 six weeks; and as it had to be exposed to the action of the atmosphere, a 



