DETERMINATION OF TRANSATLANTIC LONGITCDM. 448 



Value of ten divisions on the scale, . 



0J5 inch. 



Number of cells of Minolta's battery used at Duxbury in the longitude campaign. . 40 



Number of cells of Minotto's battery used at Brest, 





Electromotive force of the Duxbury battery expressed in Daniell's cells, . . 33.7 



Electromotive force of the Brest battery expressed in Daniell's cells, . . , |&$ 



On the nights of January 5 and 8, the mirror of the Thomson galvanometer at Dux- 

 bury was suspended by a single silk fibre at the top and bottom of the tub. < >n all 

 other occasions, the mirror was suspended by a single fibre from the top of the tube 

 the bottom fibre being cut away in order to render the needle more sensitive. 

 • As the Transit room of the Coast Survey at Brest was distant about cur quarter of 

 a mile from the cable office, it was necessary to use a Daniell's battery of live cells in 

 the local circuit which connected the key in the cable office with the chron o met- r and 

 chronograph. At Duxbury, the Transit room and cable office were only one f-ixth of 

 a mile apart, and a Daniell's battery of three cells was suflicient to work the cl< 

 and chronograph circuit. 



In order to be able to exchange signals with the Harvard College < mservaloty, (ha 

 Coast Survey station at Duxbury was joined to the Boston air-line of telegraph by a 

 loop made of the "American compound telegraph-wire," and with the office of the 

 cable line by a second loop of the same wire, which were kindly loaned by Mr. Moaee 

 G. Farmer. This wire is of the diameter known as "steel-core No. 16" its external 

 diameter being No. 13. It weighs one hundred and thirty-four pounds to the mile. 

 Its conductivity is about equal to No. 7 of galvanized iron. The distance from 

 Duxbury to Cambridge by the wire is between forty-three and forty-four milee. The 

 battery used was about fifteen bi-chromate of potash cells. .Sometimes, however, 

 thirty-five cells were required, and, at other times, ten cells were sullieient. 



The signals used between Cambridge and Duxbury were of two kinds. I. Mock- 

 signals. In this case each second break of the clock at one station not only recorded 

 itself upon the chronograph at that station, but, operating upon the main line and the 

 relay magnet at the second station, was also registered by means of the local battery 

 upon the chronograph at the latter station. In sending the signals from Duxbury to 

 Cambridge, the Krille Sidereal Clock was always used. On January 14, Profes r W .n- 

 lock reported that the signals from Duxbury were not well received when his s.dereal 

 clock was in the main circuit, so that on and after that date the Mean Time clock, 

 which broke the circuit only every alternate second, was substituted in sending clock- 

 signals to Duxbury. But the times of sending and receiving all kinds of aign Is were 

 recorded on the chronograph by the sidereal clock. The clock-signals were sent for 



