ON THE FACTS OF EARTHQUAKE PHENOMENA. 275 



point, precisely in the range with the first peg or ranging-rod, and let to 

 lie on the surface. One of the 35-foot rods was now laid down upon the 

 level sand along the line (wiiich the cord served accurately to mark), the 

 extremity of the rod being over the centre of the brass nail in the stake head. 

 Three pieces of deal board of 12 inches square each and f inch thick, were 

 provided, and one of these was placed flat on the sand with its centre under 

 the other extremity of the 35-foot rod. 



The other rod was now placed along the cord in line with the former, one 

 of its extremities being laid within an inch or so of that of the former rod, 

 and the other upon a similar piece of board (see Diag. 2). One person 



Terminal 

 stake. D . 2 . A B 



cord, r ~^ -w ae /\ 2/ ^ "^( ''"'''^ 



; 35 feet. " 35 feet. 



(Downing) stooping, now brought the ends of the two rods gently together 

 and into contact upon the board A. 



Another person (the writer) observed that the extremity of the second 

 rod upon the board B was not deranged or brought out of line in doing this, 

 and that it was not shifted until the first rod had been again applied to it in 

 advance. 



As soon as the visual contact was made at A, Downing gave the word 

 (lift), and two gunners, placed at the positions jv, x, lifted the first rod pa- 

 rallel to itself, carried it forward, and deposited it in advance with its rear- 

 ward extremity again on the board B, and within an inch or so of the second 

 rod ; the other end being laid down on the third board (C), which was carried 

 forward by another assistant in readiness, and who ran back for the board A 

 as soon as he had deposited C. Downing now again brought the rods' ends 

 into visual contact and gave the word (lift), when the rear rod was lifted and 

 carried forward by two other gunners placed at y and z ; and thus the mea- 

 surement proceeded, the rods being alternately carried forward and their 

 extremities brought into contact as described, guided in range by the cord 

 and stakes, the cord itself being strained afresh when its end was nearly reached. 



A third assistant (William Mallet) kept account of the number of appli- 

 cations of the rods, or rods' lengths, as a check upon the counting of Downing 

 and myself. The rate of progress thus made was extremely rapid, nearly if 

 not quite as fast, when the men became accustomed to it, as common chain 

 measurement, and its accuracy seemed very great. 



5280 1 320 



As there are =1320 feet in a quarter of a mile, and ' =37-1-25 



4 35 



feet, there were only 38 permutations to reach a quarter of a mile. As soon 

 as the 38th rod was laid down and brought into contact it was "let lie," and 

 then from its rearward extremity, 25 feet was counted off" along the rod, and 

 a fine string was passed across the 25 foot-mark, at right angles to the rod, 

 reaching about 6 feet each way; a stake was driven temporarily in at each 

 end of this to fi.x the string ; the string loosed and the 35-foot rod removed, 

 and the string again replaced. The intersection of this string. A, B, with 

 the ranging cord, C, D, gave then the exact spot of the termination of the 

 first quarter-mile (see Diag. 3). Both the cords were now laid aside, and the 

 permanent 6-inch square oak terminal stake driven 4 feet to a level with the 

 sand. The ranging cord and transverse string were now replaced, and at 

 their point of intersection over the stake-head a brass composition nail was 

 driven into the oak, which marked the precise termination of the first quarter- 

 mile. The measurement then of the second quarter- mile proceeded in the 



T 2 



