On the Electric Telegraph between England and India. 45 



work in the first instance from the heights of instrument (put in 

 pencil lines) and to check it afterwards by plotting from the 

 reduced heights above datum. 



It may also be observed that any errors made in the readings 

 of the staff over the stations is by this method confined to such 

 stations. The general correctness of the work depending on the 

 first readings taken after the settings of the instrument, and on 

 those last taken before changing the instrument. Such readings 

 should be taken at least two or three times each (and the staff 

 waved slowly backwards and forwards towards observer in order 

 to get the lowest readings) to ensure accuracy. 



Now, if we refer to the standard French work, entitled 

 " Manuel du Conducteur des Ponts et Chaussees" (page 109, 

 volume second) we find a system of section levelling in which 

 the back-sights and fore-sights are equal in number. This sys- 

 tem compels the operator to place his instrument in most unfa- 

 vourable positions on steep ground, and to change the positions 

 of the instrument on an average of at least four times oftener 

 than is necessary in the American system. And not only this, 

 but any error in a reading on any station affects all the subse- 

 quent readings. 



Like remarks apply to the systems published by English 

 authors. For instance, to that given by T. Baker, C.E., in his 

 work on Land Surveying, published by Virtue and Co., to the 

 system given by J. F. Heather, M.A., of the Royal Military 

 Academy, Woolwich ; and to the system recommended by Colonel 

 Frome, of the Royal Engineers, in his Treatise on Trigonome- 

 trical Surveying. 



Art. V. — On the Electric Telegraph between England and India, 

 and how to connect the Australian Colonics with the Telegraphic 

 systems of Europe and America, by E. C. Gracknell, Esq., 

 Superintendent of Telegraphs for New South Wales. 



[Eead before the Society, 14th July, 1869.] 



The time having now arrived for the joint and energetic action 

 on the part of the Australian colonists to secure to themselves 

 the benefits to be derived from telegraphic communication with 



