NATURAL PHILOSOPHY. 105 



NEW METHOD OF INCREASING THE DURABILITY OF ENGRAVED 



COPPER PLATES. 



At a recent meeting of the London Society of Arts, Mr. F. Joubert gave an 

 account of a new method of rendering engraved copper plates capable of 

 producing a greatly increased number of impressions, which consists of 

 covering the printing surface with a very thin and uniform coating or film 

 of iron. This is effected as follows . At the positive pole of a galvanic 

 battery a plate of iron is placed, and immersed in a proper iron solution, and 

 a copper plate being placed at the opposite pole, and likewise immersed, if 

 the solution be properly saturated, a deposit of iron, bright and perfectly 

 smooth, is thrown upon the copper plate. This coating ma$ be removed 

 and renewed as often as is found necessary, and thus it is stated that 12,000 

 impressions have been produced from one copper plate. 



ON THE REFINEMENT OF MECHANICAL AND ARTISTIC WORK. 



The editor of the London Literary Gazette, having recently charged Ruskin, 

 the well-known art-critic, with extravagant hypei'bole, in using in one of his 

 lectures the following expression: "Turner's pencil did not move over the 

 thousandth of an inch without meaning," the lecturer defends himself in the 

 following reply : 



So far from being an hyperbole, it is much within the truth, being 

 merely a mathematical accurate description of fairly good execution in either 

 drawing or engraving. It is only necessary to measure a piece of any ordi- 

 narily good work to ascertain this. Take, for instance, Finden's engraving 

 at the 180th page of Rogers's poems in which the face of the figure, from 

 the chin to the top of the brow, occupies just a quarter of an inch, and the 

 space between the upper lip and chin as nearly as possible ^ of an inch. 

 The whole mouth occupies one-third of this space, say ^j of an inch, and 

 within that space both the lips and the much more difficult inner corner of 

 the mouth arc perfectly drawn and rounded, with quite successful and suffi- 

 ciently subtle expression. Any artist will assure you that, in order to draw 

 a mouth as well as this, there must be more than twenty gradations of shade 

 in the touches ; that is to say, in this case, gradations changing, with mean- 

 ing, within less than the thousandth of an inch. 



But this is mere child's play compai-ed to the refinement of any first-rate 

 mechanical work much more of brush or pencil drawing by a master's 

 hand. In order at once to furnish you with authoritative evidence on this 

 point, I wrote to Mr. Kingsley, tutor of Sidney-Sussex College, a friend to 

 whom I always have recourse when I Avant to be precisely right in any 

 matter; for his great knowledge both of mathematics and of natural science 

 is joined, not only with singular powers of delicate experimental manipula- 

 tion, but with a keen sensitiveness to beauty in art. His answer, in its final 

 statement respecting Turner's work, is amazing even to me, and will, I 

 should think, be more so to your readers. Observe the successions of meas- 

 ured and tested refinement. Here is No. 1 : 



" The finest mechanical work that I know which is not optical is that 

 done by Nobcrt in the way ot ruling lines. I have a series ruled by him 

 on glass, giving actual scales from "000024 and -000010 of an inch, perfectly 

 correct to these places of decimals*, and he has executed others as fare 



* That is to say, accurate in measures estimated in mittiontlis of inches. 



