462 



MEMOIRS OF THE AMERICAN ACADEMY 



fraction of a second intervenes between the real and the recorded arrival of the 

 signal. Various elements enter into this loss of time, partly physiological, and partly 

 instrumental, as in the other case; their aggregate effect is the Personal Equation 

 in noting signals. This is not exactly the same for the two observers at the opposite 

 stations otherwise it would be eliminated by employing signals sent in both directions 

 alternately. 



Therefore, it must be determined separately for the two observers, and 



the proper allowance be made for the diffe 



A series of observations 



made by Mr. D 



January 24 and 25, in order 



determine his Personal Equation in recording Cable-Signals at Brest. The chronograph 

 w;is adjusted so that it would make two and one quarter revolutions in a minute of 



time ; one -«;con 



d of time being represented 



on the chronograph sheet by a distance 



of three quartern of an inch. A galvanometer, similar to the Thompson galvanometer 

 used in the Cable Office, was adjusted in the testing-room of the office. The cable-key 

 remained in its usual place in the instrument-room, which is at some distance from 



the testinfj-room. TV 



galvanometer and the cable-key were united w r ith a 



of Minotto's battery, and ten thousand units of resistance coils, in addition 



to the 



passed between th 



cable 



ffice and the Coast Survey Statio 



and the clock and chronograph, were introduced, the beam of light from the mirror of 



galvanometer moved in the same way 



whe 



the Second Class of cable-sig 



came from Duxbury. On January 30, the experiments were modified by placing the 

 cable-key in the testhuj-room, and substituting for the first galvanometer that very 



A 



nstrument-room by which all the longitude signals had been received, 

 of observations was made by Mr. Goodfellow on February 8, 9, and 1 



order to determine his Personal Equation in recording Cable-Signals at Duxbury. The 

 current from a Daniell's battery of three elements was sent through the clock and 

 chronograph of the transit-room of the Coast Survey Observatory, and through the 



key 



break-circuit kev 



the Cable Office 



The 



fr 



le 



and the galvanometer 



© 



cell of Minotto's battery was sent through the same circuit, 



used in receiving cable-signals from Brest was shunted so as to make it prod 



deflections similar to those observed 



the cable-sig 



The 



•o 



proceeded 



from the battery-room, and the observer who noted and recorded them was placed 

 another part of the building, out of sight and hearing of anything which occurred 



battery-room. In all these observations made at B 



and Duxbury 



the retardation in noting cable-signals, these signals were sent through the local 



hich 



the 



connects the Cable Office with the Coast Survey Station. In order to prevent 

 terference of the clock-breaks with the passage of these signals, the clock is 



