114 Mr. Henry Bradbury [May 11, 



will yield a perfectly flat and smooth surface, so that the surround- 

 ing surface of the plastic composition will be exactly level with the 

 surface of the etched stone : all that is necessary now is to prepare 

 the electrotype apparatus, by which a perfect /ac-^imzVe is produced, 

 representing the agate impressed, as it were, into a polished plate of 

 copper. This forms the printing-plate. The ink in this case, as 

 opposed to the mode before referred to, is not applied upon the 

 surface, but in the depressions caused by the action of the acid on 

 the weaker parts ; the paper is forced into these depressions in the 

 operation of printing, which results in producing an impression in 

 relief — a feature that is rather peculiar to the process, as the raised 

 appearance, especially in the case of plants, adds very much to 

 tlieir effect. 



The impressions printed in this latter manner present far more 

 beautiful and natural representations, since the crystallised quartz 

 are represented white, while the decomposed parts appear hlach. 



Professor Ley dolt, however, suggests that some corroded stones 

 are better suited sometimes for one method of representation than 

 the other ; and attention should be paid to this while the stones 

 are being exposed to the action of the acid. He considers that 

 important advantages will result to science from the perfect faith- 

 fulness of such representations, and from the facility and incon- 

 siderable expense of their production. 



Other objects in geology — such as the fossil remains of fishes, 

 plants, and other organic remains — in some cases can be, and have 

 been, copied with unmistakeable resemblance to the original. 



It is not clear who may have suggested the possibility of creating 

 impressions of these last-named objects, but one thing is beyond a 

 doubt, that the production of them was left entirely to the judgment 

 of Andrew Worring, as was also the case in the production of the 

 agates and other stones. 



In operating upon this class of objects, it is desirable that the 

 original should be as flat as possible, as the flatter the general 

 surface is, the more successful will be the effect produced. 



A mould in the first place is taken with gelatine or liquid gutta- 

 percha, the elasticity of which materials are favourable for flattening 

 the mould without distortion when separated from the original, — 

 a mode that is to be preferred to depositing copper direct upon them, 

 since it is very much more easily manipulated and without the slightest 

 risk of damaging the originals, owing to the absence of pressure. 



This gelatine or gutta-percha mould is rendered metallic or con- 

 ducting in the usual way by the application of plumbago, and copper 

 is deposited until of suflScient thickness to form a printing plate. 



In 1852, Mr. Aitken, of Birmingham, followed the footsteps of 

 Kyhl in various experiments made by him in Britannia metal. 

 He took impressions of lace, skeleton-leaves, feathers, cfec, in 

 Britimnia metal, for the purpose of ornamentation, in the same way 

 as Kyhl is said to have done in articles of silver. About this 



