THE TRANSATLANTIC LONGITUDE. 97 



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



Positive. Negative. Both. 



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



10 0'.249 9 0^242 19 0".246 



Exp. VII. 4 cells. The same. 



8 0.2G8 10 0.290 18 0.219 



Exp. VIII. 10 cells. The same. 



10 0.270 10 0.245 20 0.258 



Exp. IX. 10 cells. Resistance of 25 ohms interposed between key and galvanometer. • 

 10 0.254 10 0.258 20 256 



Exp. X. 10 cells. Resistance increased to 251 ohms. 



9 0.28'? 10 0.289 19 0.288 



Exp. XL 10 cells. Resistance increased to 2513 ohms. 



10 0.305 9 0.286 19 0.296 



Exp. XII. 10 cells. Resistance increased to 25130 ohms. 



11 0.288 10 0.299 21 0.293 



From these experiments it may fairly be concluded : — 



1. That there was no real diiFerence in the interval for the make-circuit and the 

 break-circuit signals. The mean from the first four experiments gives, after appli- 

 cation of the corrections for pass-time of the key, an interval 0'.261 for the make- 

 circuits, and 0'.260 for the break-circuits. 



2 That the relative positions of key, galvanometer, and battery exerted no 

 perceptible influence upon the result, when a battery of 4 cells was employed. The 

 mean intervals from the first two, aind from the second two experiments, are 0'.258 

 and 0'.262 respectively. 



3. That no appreciable effect was produced by the interpolation of 126 ohms' 

 resistance. The mean intervals with and without this resistance, were 0'.258 and 

 0\263. 



4. That no marked diminution of the interval was produced by an increase of 

 the battery from 2 to 10 cells. The results with 1 cell, although untrustworthy, 

 indicate a somewhat less interval. The others vary by less than their probable 

 errors, yet the interval was certainly not greater with 2 cells than with 10. 



5. From the last three experiments it would appear that the interval was slightly 

 longer after resistances above 250 ohms had been introduced. Yet it was no longer 

 in the 12th experiment, when the resistance between the key and the galvanometer 

 was more than two- thirds greater than the whole resistance of the two joined cables, 

 than in the 11th when it was only one-sixth as great as that of the tAVO cables. 



6. We have every reason for believing that in all these twelve experiments, the 

 measures of the intervals were merely determinations of my own personal equation 

 in noting signals, which, as has been shovra in Chapter IX, ha,d been found by 

 special investigation to be about 0^275. The variations from this value amount 

 in but few cases to more than ± 0\03, which we have seen to be the normal range. 



7. These experiments are entirely confirmatory of what would have been antici- 

 pated from theory, viz., that a signal given by closing a galvanic circuit is trans- 

 mitted in both directions simultaneously, and with equal velocity under similar 



13 September, 1869. 



