Etigravifig on Zinc— List of New Patents. 471 



that such a solution cannot apply to them : for when the disc 

 of the wheel, instead of being marked by a number of radiant 

 Imes, has only one radius marked upon it, it presents the ap- 

 pearance, when rolled behind the bars, of a number of radii, 

 each having the curvature corresponding to its situation ; their 

 number being determined by that of the bars which intervene 

 between the wheel and the eye. So that it is evident, that the 

 several portions of one and the same line, seen through the in- 

 tervals of the bars, form on the retina the images of so many 

 different radii. 



The true principle, then, on which this phsenomenon de- 

 pends, is the same as that to which is referable the illusion that 

 occurs when a bright object is wheeled rapidly round in a circle, 

 giving rise to the appearance of a line of light throughout the 

 whole circumference; namely, that an impression made by a 

 pencil of rays on the retina, if sufficiently vivid, will remain for 

 a certain time after the cause has ceased. Many analogous 

 facts have been observed with regard to the other senses, 

 which, as they are well known, it is needless here to particu- 

 larize. — Phil. Trans. 1825. 



ENGRAVING ON ZINC. 



There has lately been published by Leske the bookseller, 

 at Darmstadt, the first large work of which the })lates are exe- 

 cuted in zinc. It is a collection of monuments of architecture, 

 which will consist of twenty numbers. The work is done on 

 zinc in the same manner as on stone, and the expense of en- 

 graving is thus avoided : hence the publisher has been enabled 

 to sell the number, consisting of twelve folio plates, at five 

 francs upon common paper. In an economical point of view, 

 this method, therefore, deserves to be recommended. We see 

 by the German journals, that M. Eberhard, author of the 

 collection in question, has recently published a pamphlet upon 

 the use of zuic, with tiie view of replacing copper-plates and 

 lithographic stones, for engraving and designing. 8vo, with 

 10 plates. (Darmstadt, 1824.) Edin.Phil.Jown. 



LIST OF NKW PATENTS. 



To William Henry James, of Coboiirg Place, Winsori Green, near 

 Birmingham, engineer, for improvements in apparatus for diving under wa- 

 ter, and a|)plicable to other purposes.— Dated 31st May 1825.— 6 months 

 to enrol specification. 



To .John Harvey Saciler, of Hoxton, Middlesex, muchini.st, lor an ini- 

 nrovcd power-loom for the weaving of silk, cotton, linen, wool, flax and 

 hemp, and mixtures thereof — ."Mst May. — (i months. 



To .Joseph I'Vcderick l.edsam, merchant, and I^enjamin Cook, l.rass- 

 founder, both of Birmingham, for improvements in the production and 

 purification of coal gas.- .'Jlst May.— fi monlhs. 



To 



