72 



NATURE 



{May 27, 1875 



345, Strand, the magnetic disturbances and interference 

 with transmitted signals from auroras and earth-currents 

 were first observed and the observations tabulated, which 

 have since proved useful, notwithstanding the then defec- 

 tive construction of the recording apparatus ; here also the 

 earliest lines of railway telegraph were inaugurated ; the 

 long five-inch astatic combination of the double needle 



and single needle instruments was employed, taking the 

 place of less perfect apparatus. It must be remembered 

 that, previous to the introduction of the double and single 

 needle instruments, very cumbersome apparatus had been 

 employed. There was the five-needle instrument, requir- 

 ing five wires for the five needles, and a sixth wire for the 

 return current (Cooke and Wheatstone's patent, 1837) ; 



Fig. 27.— Wheatstone's letter-showing dial telegraph, 1840. 



the respective letter or signal being indicated by the 

 concurrent deflection of two pointers. Obviously, this 

 instrument became useless for extended circuits, the 

 eapital cost of outlay for the six wires restricting its use. 

 The old letter-showing apparetus of Cooke and Wheat- 

 stone ( 1 840), in which the letters of the alphabet composing 

 the word are severally presented to view at an opening in 

 a dial-plate by means of an electro-magnet acting upon 

 the pallets of an escapement, put in motion by inde- 



pendent clockwork. The communicator of the instrument 

 is furnished with a dial-plate similar to that of the indi- 

 cator, so that on the rotation of the dial of the communi- 

 cator by the operator, the necessary succession of make 

 and break currents of electricity are sent through the wire 

 and controlled so as to actuate the motion of the index- 

 pointer of the indicator at the distant station. 



{To be continued^ 



THE INDIAN TRIGONOMETRICAL SURPEV* 



ONE does not usually expect to find much of general 

 interest in the Report of a Trigonometrical Survey. 

 Col, Walker's admirably drawn-up Report, however, in- 

 cludes some matter of more than special value ; indeed, 

 many of the details connected with the immediate work 

 of the Survey are calculated to interest the general reader, 

 they are concerned to such a large extent with the peculiar 

 difficulties to be overcome by the various parties, difficul- 

 ties which make ordinary survey work look like mere 

 child's play. 



The Index Chart prefixed to the Report enables one to 

 form a very full idea of the work which has already been 

 done, and of how much there is yet to do. From Cape 

 Comorin to Peshawur and all along the Himalayan fron- 

 tier, and from Kurrachee on the west to Burmah on the 

 east, the country is covered with an intricate net- work of 

 triangulation, including, however, many gaps which will 

 take many years to fill up. Shooting out from the 

 northern border of the system of triangulation are nume- 

 rous aurora-like lines indicating the secondary triangula- 

 tion to fix the peaks of the Himalayan and Sooliman 

 ranges. We cannot go into the details of the work of the 

 Survey, and must content ourselves with a brief summary 

 of the out-turn of work during the year under review, and 

 with a reference to a few of the more interesting side 

 topics. 



Of Principal Triangulation, with the great theodohtes 

 of the Survey, seventy triangles, embracing an area of 



* General Report of the Operations of the Great Trigonometrical Survey 

 of India, during 1873-74, by Col J. T. Walker, R.E., F R.S., Superinten- 

 dent of the Survey (Dehra Dun ; Office of the Superintendent, G. T. 

 Survey, M. J. O'Connor, 1874.) 



7,190 square miles, and disposed in chains which, if 

 united, would extend over a direct distance of 302 miles, 

 and in connection with which three astronomical azimuths 

 of verification have been measured. Of Secondary Trian- 

 gulation, with vernier theodolites of various sizes, an area 

 of 5,212 square miles has been closely covered with points 

 for the topographical operations, an area of 3,650 square 

 miles has been operated in pari passu with the principal 

 triangulation but exterior thereto, and in an area of 1 2,ocx3 

 square miles— in the ranges of mountains to the north of 

 the Assam Valley which are inhabited by independent 

 tribes — a large number of peaks have been fixed, many 

 of which have already been found serviceable in the geo- 

 graphical operations now being carried on with the mili- 

 tary expedition against the Dufiflas. Of Topographical 

 Surveying, an area of 534 square miles has been com- 

 pleted in British portions of the Himalayas, on the scale 

 of one inch to the mile, an area of 2,366 square miles in 

 Kattywar on the two-inch scale, and areas of 690 and 63 

 square miles respectively, in Guzerat and in the Dehra 

 Dun, on the scale of four inches to the mile. Of Geo- 

 graphical Exploration much valuable work has been done 

 in Kashgharia and on the Pamir Steppes, in connection 

 with Sir Douglas Forsyth's mission to the Court of the 

 Atalik Ghazi, and several additions to the geography of 

 portions of Great Thibet and of Nepaul have been 

 obtained through the agency of native explorers. 



In the course of the operations of the year under review 

 the northern section of the Brahmaputra Meridional Series 

 has been completed, whereby two important circuits of 

 triangulation formed by it with the Assam and East Cal- 

 cutta Longitudinal Series to the north and south, the 

 Calcutta Meridional and the Eastern Frontier Series to 



