HEADQUARTERS OF SURVEY DEPARTMENT. 229 



doubt, as time goes on, it will be much more largely employed for 

 map work. 



The process of electro typing was first introduced in connexion 

 with the photo-electrotype process of heliogravure about 1882, 

 and has proved very valuable in connexion with that process, and 

 also as an economical means of duplicating engraved plates of 

 standard maps in various stages of their progress, in order to 

 obtain skeleton maps with varying amounts of detail, suitable for 

 the illustration of reports and other administrative purposes. It 

 has also been found very useful in carrying out extensive cor- 

 rections on the engraved plates ; a matrix being made from the 

 original plate, the parts in relief corresponding to the parts to be 

 corrected are scraped away and a duplicate plate is electro typed on 

 which the faulty parts present a blank flat space upon which the 

 new details required can be engraved. The process is scarcely ever 

 used, as it is at the Ordnance Survey Office, Southampton, for 

 producing printing plates, as the process of steel-facing which 

 enables the original engraved plates to be printed from without 

 injury has been found to be cheaper and more suitable for the 

 requirements of the Indian Office. 



The electrotyping method in use is practically the same as was 

 practised for many years at the Military Geographical Institute in 

 Vienna, and consists of a horizontal single-cell apparatus in which 

 an electrical couple is formed by the copper plate to be deposited 

 on, which rests on a suitable support in a bath of sulphate of 

 copper, and an iron plate immersed in dilute sulphuric acid, 

 contained in an upper tray with a leathern bottom which forms 

 a porous diaphragm. These batteries are found to work with 

 regularity and practical economy, being very simple in working and 

 easily looked after by natives. The electrotyping work is done 

 in the Photographic Office. 



Probably the most important cartographical work of the Calcutta 

 Office is the Indian Atlas. This great work is on the scale of four 

 miles to the inch ; it is the standard map of India, and embodies the 

 results of the detailed surveys. It is designed to cover 181 full 

 sheets, 40 inches by 27, on the globular projection and scale 

 originally proposed by Mr. Aaron Arrowsmith, and the region 

 embraced extends from Karachi to Singapore and from Gilgit to 

 Cape Comorin. It also includes Ceylon. The original sheets, for 

 which the Madras Topographical Surveys furnished the materials, 



