1878.] to the Reproduction of BLips and Flans. 101 



the images produced on the metal plates. In like manner, the earliest appli- 

 cation o£ the peculiar action of the alkaline bichromates upon colloid 

 substances was Fox Talbot's photoglyphic process, which was soon followed by 

 the photo-gal vanographic and helioplastic processes of Pretsch and Poitevin. 

 Engraving processes have also been based upon Swan's pigment-printing 

 process, the Woodbury-type and the collotype. With the exception, 

 perhaps, of the second, all these methods, from the earliest to the latest, are 

 in use at the present time in a more or less modified form. 



The object of engraving maps upon copper is to obtain a plate taking 

 but little storage room and not liable to break, which shall yield a large 

 number of impressions of uniform quality and, with due precautions, be 

 capable of being preserved in a good condition for printing during any 

 length of time. 



Copper-plates have the further advantage that they may be multiplied 

 to any extent by eleetrotyping, and corrections may be made when required, 

 either on the original plate or on the electrotyped matrix or copy. Transfers 

 may also be made from them to stone or zinc and printed in the same way 

 as ordinary lithographs. This procedure is specially applicable when very 

 large numbers are required or when the subject is to be printed in colours. 



Besides these more practical advantages, the superior beauty and finish 

 of copper-plate engraving give it the preference for all maps of a permanent 

 or standard character. 



With these objects in view nearly every civilised nation has at least 

 one engraved map giving the results of the State Surveys on a convenient 

 scale for general use. For the same reasons map-publishers generally 

 engrave the maps composing their atlases and other standard publications. 



Notwithstanding its many advantages copper-plate engraving is a 

 very slow process and is also expensive, because the art of the engraver is 

 one requiring great artistic and manipulative skill, only to be fully acquired 

 by an almost life-long apprenticeship. Map-engraving, it is true, does not 

 require so high a degree of artistic skill as line or aquatint engraving, but 

 it nevertheless requires a long training, particularly in the more difficult 

 branch of hill-etching which demands almost as much skill to produce 

 first-rate results as ordinary line-engraving. 



Although the advantages of photographic engraving as a means of 

 avoiding the long and costly labour of engraving maps by hand are obvious, 

 for various reasons these processes have not yet come into general use. A 

 successful commencement has, however, been made by the Italian and 

 Austrian Governments of employing photography in the production of 

 their engraved maps, and there is little doubt tliat before long, photographic 

 engraving will be more extensively used for this purpose than it is at pre- 

 sent, especially as processes arc now available by which gradation t)f shade 

 14 



