THE TRANSATLANTIC LONGITUDE. 



85 



D. ■ No GROUND-CONNECTION WHATEVER. 







From 



Positive Signals. 



From 



Negative Signals. 



No. 



Excess for 







No. 



Mean interval. 



Nb. 



Mean interval. 



cells. 



positive. 



Yalencia signals. 

















November 1, 



1.3, 



9 



2" 52"14M12 



9 



2h 52'"14M22 



20 



—0^010 



5, 



Longit. 



29 



n.294 



29 



17.294 



3 



0.000 



6, 



" 



18 



11.203 



16 



17.214 



3 



—0.011 



9, 



" 



30 



20.292 



28 



20.290 



4 



+ 0.002 



10, 



L3, 



10 



20.748 



10 



20.790 



4 



—0.042 



10, 



II. .s. 



9 



20.T52 



10 



20.821 



4 



—0.069 



16, 



IV. 3, 



9 



21.157 



10 



21.161 



4 



—0.004 



Newfoundland signals. 















Novembei- 5, 



Longit. 



30 



18.465 



28 



18.482 



3 



—0.017 



6, 



" 



20 



18.302 



20 



18.312 



10 



—0.010 



9, 



" 



30 



2L369 



30 



21 365 



10 



+ 0.004 



10, 



IL 1, 



10 



21.902 



10 



21.915 



20 



+ 0.013 



10, 



II. 2, 



10 



21 926 



10 



21.939 



20 



+ 0.014 



10, 



II. 3, 



10 



21.922 



10 



21.918 



20 



—0.004 



16, 



III. 3, 



10 



22.285 



10 



21.277 



4 



—0.008 



16, 



IV. 3, 



9 



22.281 



10 



21.266 



4 



—0.021 



Our mean values have here been recorded to thousandths of a second — a degree 

 of precision which is of course only nominal, since the accuracy attainable by the 

 mode of observation employed would scarcely warrant any reliance even upon the 

 second decimal for the mean of a number of observations much larger than ten. 

 Yet, if this be borne in mind, no error can result from the employment of three 

 decimals; while, on the other hand, -this affords a reciprocal control in the figures. 



It is manifest that if we disregard the signals given from Valencia while the 

 zincode was connected with the ground on the 10th November, all the differences 

 are of an order of magnitude which justifies the assumption, already probable from 

 theoretical considerations, that the positive and negative signals travel with equal 

 velocity under the same circumstances. This assumption I will therefore make, 

 postponing any remarks concerning the discordance manifested on the 10th 

 November. 



The speed of the two kinds of signals being thus taken as the same under simi- 

 lar circumstances, the time required for their transmission is easily deduced, being 

 one-half the difference between the measures of longitude as derived from the 

 records at the respective stations. The weak point in our determination is, of 

 course, the absence of any automatic record of signals received ; but the considera- 

 tions already presented in tbe chapter on Personal Error in Noting Signals afford 

 ground for confidence that the uncertainty here introduced is comparatively small, 

 and that the aggregate personal error of the two observers is very close to 0'.606. 

 This value is adopted in the present investigation, and all the measurements herein- 

 after recorded, with which this personal error is merged, have been corrected by 

 deducting this quantity. 



Then for a circuit formed by both cables, without earth-connection, we have the 

 following determinations of the sum of the transmission-times for eastward and 

 westward signals, derived from the last three series of longitude-determinations, and 

 from the second and fourth series of special experiments. 



