158 ANNUAL OF SCIENTIFIC DISCOVERY. 



interpolation of any resistance between them and the gal- 

 vanometer be made to traverse the double length of the cable 

 before reaching the galvanometer at the same station. 



The construction of the signal-key used in these experiments 

 was such that only about one-seventieth of a second was oc- 

 cupied in pressing down the button. All signals by which 

 currents were sent were given in this way, but the break-circuit 

 signals were given by removing the thumb from the button, 

 which was then lifted by the tension of the spring. This tension 

 being less than the muscular force of the thumb when the 

 button was pressed down, a longer time was consumed in trav- 

 ersing the distance between the stops, and for this repeated 

 experiments give 0.035 s as a near approximation to the average 

 interval. Now, since the ordinary signals record themselves 

 upon the chronograph when the arm carrying the button leaves 

 one stop, but are not really given until it reaches the other, all 

 the recorded intervals between the instants of giving and receiv- 

 ing make-circuit signals will be too large by about one-seventieth 

 of a second, or approximately 0.015 s ; while for break-circuit 

 signals the reverse obtains, and the recorded interval will be too 

 small by about 0.035 s . Consequently, in comparisons between 

 break-circuit signals and others, a correction must be applied, 

 varying with the temporary adjustment of the signal -key, but 

 amounting on the average at Valencia to not far from 0.05 8 . This 

 correction must be borne in mind in drawing inferences as to the 

 relative velocity of break-circuit and make-circuit currents. Dr. 

 Gould does not apply it in his tallies, however, because no 

 measurements were made to determine the pass-time for the 

 Newfoundland key. 



In these experiments the circuit was formed of the two cables 

 with no other connections than the same ke}^, galvanometer, and 

 battery at Valencia which had been employed for the other work 

 of the expedition. 



Exp. I. 4 cells. Circuit made and broken. Key between Zincode and gal- 

 vanometer. 



No. Mean Interval, 



Make circuits, 11 0.257s 



Break circuits, 11 0.229 



Exp. II. 4 cells. The same with 126 ohms' resistance between key and gal- 

 vanometer. 



Make circuits, 10 0.279 



Break circuits, 9 0.227 



Exp. III. 4 cells. Key and galvanometer upon opposite sides of the battery. 

 Make circuits, 13 0.278 



Break circuits, 14 0.225 



Exp. IV. 4 cells. The same with 126 ohms' resistance between key and cable. 

 Make circuits, 11 0.278 



Break circuits, 11 0.220 



Exp. V. 1 cell. Positive and negative signals. 



Positive. Negative. Both. 



No. Mean. No. Mean. No. Mean. 



2 0.240 8 0.292 10 0.282 



Exp. VI. 2 cells. Positive and negative signals. 



10 0.249 9 0.242 19 0.246 



