2 Correction of Engraved plates hy Electro-deposition. [Jan. 



The President announced that the lectures to he given during the 

 month of January, woukl be — 



On the 14th, by the Hon. J. B. Phear— " On Glimpses of Old India 

 as seen through the pages of Manu." 



On the 28th, by Mr. H. F. Blanford— " On the Winds of Northern 

 India." 



The following papers were read : — 



1. On a Secondarif Sexual Character in Sqiiilla rapliidea, Fabr. — Bi/ 

 J. Wood- Mason Esq. 



This note will be included in a paper on Indian sguillidcje. 



2. On tlie application of Electro-deposition to tlie Correction of En- 

 graved Copper plates. — By Capt. J. Wateehouse, Assistant Surveyor 



General. 



Those acquainted with the practical details of the production of copies 

 of maps, plans or drawings by lithography or engraving, are only too well 

 aware of the necessity for making alterations on the stones or plates, either 

 for the correction of mistakes and carrying out changes made during the 

 progress of the work, or for the insertion of additional details in successive 

 editions after it is completed. 



In engraving or lithographing copies from pictures or drawings, correc- 

 tions are seldom necessary if the engraver or lithographer possesses the 

 necessary skill, and has been furnished with a properly finished drawing to 

 copy from ; but in the case of geographical maps, the constant changes of 

 boundaries, and the opening of railways, canals, roads and other administra- 

 tive improvements, necessitate continual alterations of the plates in order 

 that they may be correct and complete at the time of their publication. It 

 is always undesirable to make these corrections on a finished map, but when 

 necessary they may be made without difficulty on a stone or zinc plate, 

 because the drawing is only on the surface and can be easily removed ; on 

 an engraved copper-plate however, it is a different matter, because the lines 

 forming the drawing are cut deep into the metal and must be erased entirely 

 before any alteration can be made, leaving a hollow which has to be filled 

 up again in order that the even surface of the plate may be restored and 

 made fit for the new work to be re-engraved. 



The usual way of doing this is by what is technically called " hnoclcing 

 z^," i. e., carefully hammering the plate from behind on a polished steel 

 anvil till the hollows are filled up, and the surface of the corrected parts of 

 the plate perfectly even with the rest. 



This method is simple but has two great defects — 



1st. However neatly and carefully the knocking up may be performed , 



