222 Observations on the direction and Intensity of the [April 



arrangements with Mr. Caldecott, as to the parts we should each take in 

 the labour; when it was eventually agreed that I should undertake the 

 observations on the eastern, and that Mr. Caldecott should make those 

 upon the western, coast. 



For this purpose I left Madras on the 23d day of July 1837, and pro- 

 ceeded to the southward, making observations every day, at intervals of 

 about twenty-five miles ; until on the 2d August I arrived at Tranquebar. 

 Here I was met by Mr. Caldecott, whose zeal in the cause would not 

 allow me to make my own observations unassisted. In the observations 

 for dip, I had hitherto only found time to employ three out of the four 

 needles supplied, viz. Nos. 1, 2 and 3; but tbe presence of Mr. Calde- 

 cott suggested the propriety of employing the remaining needle (No. 4), 

 and of taking a double set of observations. This would have been 

 accomplished, but that a few preliminary trials at Tranquebar with 

 needle No. 4, convinced us of its utter uselessness for the purpose in- 

 tended, in consequence of the want of roundness of the steel pivots. 

 This discovery led to a minute examination of the other needles ; when 

 No. 2, (which had in the course of observation exhibited singularly 

 discordant rtXults), appeared likewise to differ from a cylinder in the 

 form of its pivots. These circumstances naturally led to the rejection 

 of the observations hitherto made with needle No. 2, and the wow-em- 

 ployment of No. 4 in the remaining parts of the work. But, before 

 proceeding further, I may as well give some 



Account of the Instruments employed. 



They consisted of a dip apparatus by Gilbert, furnished with four needles 

 (two useless) of 4| inches in length ; a pocket chronometer by Arnold, 

 and three intensity needles. The dipping needles were apparently cut 

 out of flat plates of steel, and were hardened at the ends (see fig. 1) ; 

 the agate planes, Ys for centering, and levels, &c. &c. differed in no 

 respect from the ordinary construction. The intensity needles I had 

 caused to be constructed here, after the plan of Captain Bethune's, to 

 agree nearly with the model of those of Professor Hansteen ; viz. each 

 needle was 2,7 inches in length, and 15 inches in breadth, cylindrical, 

 and rounded at the ends ;* they were first turned in a lathe, from pieces 

 of English steel wire, and then hardened by plunging them, when at a 

 pale red heat, into cold water ; after which they were softened in the 

 middle by placing them upon a red-hot poker. They were now mag- 



^Pidfessor Hansteen's were pointed at the ends. 



