relation to Electrical and Magnetic Phenomena, 



141 



currents, but simply to their variations ; so that a constant cur- 

 rent of any origin would have no influence on the results. 



But in these researches there is a source of error which could 

 not be neglected; that is, the influence of temperature on the 

 line-wires. This may be regarded from a twofold point of 

 view : (1) the current itself may be considered to be thermo- 

 electric in virtue of the solar action on the wire ; (2) a variation 

 of resistance in these wires, due to the temperature, may make a 

 constant current appear periodical. Thus the current from 

 Rome to Anzio, although constant, might appear variable. 



To resolve this difficulty, it seemed to me that the use of two 

 wires at right angles, one in the meridian and the other in the 

 parallel, would give sufficient elements; for, these two wires 

 being subjected to almost the same thermal variations, the 

 resulting difference ought to have the same phases. Only 

 having at my disposal the meridional wire, I requested M. Jaco- 

 bini, Inspector of Telegraphs, to be good enough to use his 

 leisure and the intervals of inactivity of a line directed towards 

 the east, and to compare it simultaneously with another directed 

 in the meridian to see if they presented notable differences. 



M. Jacobini commenced then a series of observations between 

 Rome and iVrsoli, a station to the east of Rome, 50 kilometres 

 distant, in the Apennines, and which is at right angles to the 

 magnetic meridian. Observations were simultaneously made 

 on the line from Rome to Anzio, 52 kilometres in length and 

 on the magnetic meridian, the same line as is used for the Obser- 

 vatory. After several preliminary trials, a regular system of 

 observations was arranged towards the end of May ; I give here 

 the results of the first half of June from the 1st to the 16th, 

 excluding, however, the days 7, 8, 9, and 10 ; for on these days 

 there was a strong magnetic disturbance, and currents in all 

 directions traversed the wire in a very abnormal manner, to 

 which I shall afterwards revert. 



Currents observed on the Telegraphic Wire from Rome to 

 Arsoli and to Anzio. 





6 A.M. 



7. j 8. I 9.\ 10. 



ll.|f d - 1p.m., 2. i 3. 

 day. '• ': 



Arsoli, E... 

 j Anzio, S... 



170 



200 



1 



24°ol260 18°-6J 16-2 

 180J20-5 21-0 22-0 



1 



140 116! 1°40 | 17 19-5, 

 22-4 220 20-5 j 20-3| 180 





M *■ 



6. 



7. 



8. 9. 



10. 1 11. 



Mid- j 



night, 



Arsoli, E... 

 Anzio, S.... 



180 18-0 

 17-5 170 



o ! 



19-0; iti-o 



180 20 



160 

 190 



190 

 190 



200 | 19 

 20-0 j 20-5 



I 

 230 ; 

 20-5 j 



