NATURAL PHILOSOPHY. 159 



of the drawing are very close together, a thin coat will suffice. After 

 this ground has been applied, the plate or glass has to be submerged 

 in water for about ten or fifteen minutes ; then a strong stream of wa- 

 ter is poured upon it, which will remove the waxy substance above the 

 lines of the drawing;, but will leave that between the lines undisturbed. 

 In most cases, the grounding will be sufficiently high to insure a good 

 electrotype for printing ; but where considerable height is required be- 

 tween lines far apart, this can readily be effected by applying wax ac- 

 cording to the method now employed by stereotypists, or by adding as- 

 phaltum with the brush. Should the artist prefer to make his drawing 

 on paper, the latter must first be rendered water-proof; and after it 

 has undergone this process, it should be attached, with a water-proof 

 paste, to a hard and even plate before it is covered with the wax ; in 

 all other respects, it is treated in the manner just described. Before 

 taking the electro deposit the plate must be covered with alcoholic 

 varnish, and when dry, black-lead plumbago is applied with a soft 

 brush. 



" The advantages of the process are stated by the inventor to be 

 The obtaining a perfect fac-simile of the artist's work ; the drawing has 

 not to be reversed, as in the methods now in use for copying on the 

 wood pictures or objects ; cheapness, and saving of time." 



New Process of Engraving. The following new process has been 

 devised by M. Dalos, of Paris : A plate of copper is covered with a 

 varnish of india-rubber and zinc-white. Lines are traced through this 

 surface down to the metal by an ivory point. The plate is then 

 plunged in a solution of hydrochlorate of ammonia, the positive elec- 

 trode being a plate of iron in communication with the negative pole 

 of the pile. Iron is deposited on all the parts of the copper exposed by 

 the ivory point, but not on the varnish, which is removed by benzine. 

 The plate is once more exposed to electric action in a bath of silver, 

 and that metal is precipitated on the copper but not on the iron. It is 

 then heated to 80 C., and an alloy, fusible at that temperature, is 

 poured over it. The liquid moistens the silver and adheres to it, but 

 not to the iron, which it does not moisten. When cold, the fusible 

 alloy will be found standing on each side of every line, and forming a 

 mould, from which a new plate, adapted to printing, is obtained by a 

 galvanoplastic process. 



DESIDERATA IX SCIENCE AND ART. 



The London Society of Arts proposes annually a list of subjects for 

 invention, discovery, or explanation, for the attainment of which it of- 

 fers medals, or money premiums, varying in amount from Si 00 to $500. 

 From the list proposed for this year, 1864, we copy such of the sub- 

 jects as seem to us most important and suggestive, and as best illustra- 

 tive of the more practical wants of the present epoch. 



Goldsmith's Work. For the best essay on ancient goldsmith's 

 work. 



Bronzes. - - For the best essay on the manufacture and casting of 

 bronzes, and on bronze washes. 



^Loulds for Metal Casting. For the production of a material to be 

 used in the formation of moulds for casting bronzes and other molten 

 metals, so as to enable the casts to be produced without seams. 



