4 



May 1 7, 1 848. Of these days of observation, however, six are incomplete, 

 viz., May 17, 19, 20, 23, 24, 30 ; and another day (May 27) appears, 

 from the Dublin observations, to have been a day of considerable mag- 

 netic disturbance. Omitting these, as unsuited to furnish true mean 

 results, the means of the remaining days are as follow. The positive num- 

 bers indicate currents proceeding towards Derby, and the negative, 

 currents in the contrary direction : — - 



Table II. — Mean observed Values of the Intensity of the Currents, tra- 

 versing the Wires uniting Derby and Rugby, and Derby and Bir- 

 mingham^ respectively. 







Derby and Rugby. 







Derby and Birmingham. 







Hour. 





















































A. 



M. 





p. 



M. 





A.M. 



p. 



M. 







1 



- 1-4 



0-3 



- 5 



•0 



- 5-1 



0 



•2 



1-5 



- 91 





8 



5 



2 



2-5 





~ 5 



•5 





2 



•9 





- 7-7 









3 



1-6 



1-7 



- 2 



■7 



- 3-3 



0 



•9 



1-3 



- 7-4 





7 



4 



4 



1-1 





- 2 



•4 





0 



•7 





- 7-2 









6 



0-5 



1-2 



- 1 



■8 



- 2-3 



0 



•6 



1 -2 



- 3-6 





6 



1 



6 



2-7 





- 3 



•2 





2 



•8 





- 6-3 









7 



3-1 



3-0 



- 0 



•6 



- 1-1 



3 



•9 



4-1 



- 4-5 





4 



7 



8 



31 





- 0 



•2 





5 



•9 





- 3-4 









9 



2-4 



1-8 



0 



•4 



0-2 



4 



•2 



3-4 



- 0-8 





I 



7 



10 



- 0-9 





0 



•1 





- 0 



•6 





- 1-7 









11 



- 4-3 



- 3-6 



0 



•4 



0-6 



- 7 



•2 



- 5-8 



0-3 





0 



4 



12 



- 5-1 





1 



•7 





- 8 



•1 





2-8 









It will be observed that the changes indicated by these numbers are 

 very systematic. In the wire connecting Derby and Birmingham the 

 carrent flows southwards from 10 a.m. to 10 p.m. inclusive, and north- 

 wards during the remaining hours. In the wire connecting Derby and 

 Rugby, the southward current lasts from 10 a.m. to 8 p.m. inclusive, 

 and it is northward (with a single exception) during the remaining hours. 

 There are, however, as might be expected in so short a series, some 

 irregularities in the course of the changes. In order to lessen these, 

 and at the same time to confine the results to such as are comparable 

 with the preceding, I have given (in the alternate columns of the Table) 

 the means corresponding to the alternate hours, commencing at 1 a.m., 

 computed by the formula 



i(a + 26 + c). 



The numbers so obtained are projected into curves in the diagram 

 (Plate I.), having been previously multiplied by constant coefficients, in 

 order to equalize the ranges with those of the computed results. The 

 dotted lines, in both cases, are the corresponding projections of the cal- 

 culated results. The agreement between these two sets of curves is pro- 

 bably as great as could be expected in the results of so short a series of 



