NATURAL PHILOSOPHY. 159 



Positive. Negative. Both. 



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



Exp. VII. 4 cells. Same. 



8 0.268 10 0.290 18 0.279 

 Exp. VIII. 10 cells. Same. 



10 0.270 10 0.245 20 0.258 



Exp. IX. 10 cells. Resistance of 25 ohrns interposed between key and gal- 

 vanometer. 



10 0.234 10 0.258 20 0.256 



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



9 0.2S7 10 0.289 19 0.288 

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



10 0.305 9 0.28G 19 0.296 

 Exp. XEI. 10 cells. Resistance increased to 25,130 ohms. 



11 ' 0.288 10 0.299 ' 21 0.293 



From these experiments it may fairly be concluded : 



1. That there was no real difference in the interval for the 

 make-circuit and break-circuit signals. The mean from the first 

 4 experiments gives after application of the corrections for 

 pass-time of the key, an interval 0.261 8 for the make circuits, and 

 0.260 s 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 2 

 and from the second 2 experiments are 0.258 s and 0.262 s respec- 

 tively. 



3. That no appreciable effect was produced by the interpolation 

 of 126 ohms 1 resistance. The mean intervals, with and without 

 this resistance, were 0.258 s and 0.263 s . 



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 inter- 

 val was certainly not less with 2 cells than with 10. 



5. From the last 3 experiments it would appear that the in- 

 terval was slightly longer after resistances above 250 ohms had 

 been introduced. Yet it was no longer in the twelfth experiment 

 when the resistance between the key and galvanometer was more 

 than two-thirds greater than the whole resistance of the 2 joined 

 cables, than in the eleventh, when it was only one-sixth as great 

 as that of the 2 cables. 



6. We have every reason for believing that in all these 12 ex- 

 periments the measures of the intervals were merely determina- 

 tions of my own personal equation in noting signals, which, as 

 has been shown in Chapter IX., had been found by special inves- 

 tigation to be about 0.275 s . The variations from this value amount 

 in but few cases to more than 0.03 s , which we have seen to be the 

 normal range. 



7. These experiments are entirely confirmatory of what would 

 have been anticipated from theory, namely, that a signal given 

 by closing a galvanic circuit is transmitted in both directions 

 simultaneously, and with equal velocity under similar circum- 

 stances; so that under no ordinary practicable circumstances 



