1-83.2.] Scientific Intelligence. 71 



V. — Scientific Intelligence. 

 I,— Progress of the Indian Trigonometrical Survey. 

 Plate I. 

 The measurement of the base line on the Barrackpur road was completed on 

 the 21st January, and it is difficult to imagine that any similar work was ever 

 brought to a more successful issue. Through the politeness of Captain Everest, 

 the Surveyor General and Superintendent of the Trigonometrical Survey, we enjoy- 

 ed the advantage of an invitation to witness the remeasurement of the first day's 

 work, with the view of ascertaining what might be the probable amount of error : on 

 which occasion the President of the Physical Class of the Asiatic Society and many 

 distinguished officers of the Engineer department were present. An elegant break- 

 fast was laid out in tents after the ceremonies of the morning were concluded. 

 While contemplating with admiration the order and precision with which the 

 whole process was conducted, we took an opportunity of sketching the apparatus 

 as it stood, that the readers of the Journal might be better able to comprehend 

 the nature of the operation of measurement, which was partially described in the 

 Gleanings for November last. 



Plate I. represents- the six sets of bars resting upon their tripods, levelled, and in 

 the act of adjustment, longitudinally, by means of the directing or boning telescope, 

 to the left hand. The boning telescope ought to have been considerably more dis- 

 tant from the bars, but it would then necessarily have been excluded from the 

 drawing A movable covering of tent- frame work protects the bars from the in- 

 fluence of the morning sun ; at their left extremity is seen a cast-iron tripod, firm- 

 lv imbedded in the ground, bearing a brass vertical cylinder and plate, upon the 

 surface of which is the minute dot which marks the termination of the last, and 

 acts as the starting point of the present measurement : by the adjustment of the 

 cross wires of the end microscope in the true vertical line bisecting the dot. These 

 apparatus are represented on a larger scale in the foreground ; as also one of the 

 wooden boxes containing the compound bar, shewing the two projecting tubes, 

 within which lie the cross levers of the compound bars, upon which are engraved 

 the dots, or marks to be read off by the double microscopes interposed between 

 each box, as described on a former occasion, and as will be readily comprehended 

 by reference to the drawing. The right extremity of the line is seen to enter the 

 door of the tower, where it terminated in a coincidence with the original dot, en- 

 graved upon a metallic disc attached to a sunken stone pier. 



As it had been anticipated that the settling of the masonry of the tower might 

 derange the terminal mark, precautions had been taken in the first instance to 

 sink into the ground another adjusting point at a short distance in advance of the 

 tower ; and it was in fact to this point that the remeasurement was referred, to 

 know the probable amount of error in measuring, as well as whether the tower 

 had altered its position in any perceptible degree. 



From conversation with the officers on the ground we picked up the following 

 particulars regarding the Barrackpur base. We must crave their indulgence if our 

 memory leads us into any mistake in detailing them. 



The measurement commenced on the 23rd November 1831, and ended on the 21st 

 January 1832, an interval of 58 days, of which 13 may be set down as holidays ; 

 so that the actual time employed was about 45 days. The length of the ground 

 measured upon an average was 750 feet, or 12 sets of bars : but towards the con- 

 clusion, so systematic had become the arrangements, that 18, 20, and once 24 sets 

 (that is 1512 feet) were measured in one day, which is double what was effected on 



