144 



M. Secchi on Earth Currents. 



Here the last column contains the mean temperature of each 

 month, and a proportional correction of 09 must be applied for 

 each degree of thermometric variation. But even after this cor- 

 rection the months of November and December are signalized 

 by an enormous increase in the absolute value of the horizontal 

 component, which I can also verify in the observations of Lisbon, 

 and which I think general, and which has obliged us to change 

 the scale. 



As regards the diurnal variation, the minimum is seen to 

 correspond to the maximum of the equatorial current, and in 

 the summer season the two instruments exhibit after midday 

 a secondary oscillation which disappears in winter. 



Lastly, I shall adduce the results of the atmospheric electri- 

 city obtained with the moveable conductor in the same period of 

 observations. I must first remark that for their absolute value 

 the numbers must be referred to the unit of measure in the last 

 column, dividing them by this number. M. Volpicelli, in a Note 

 printed in the Comptes Rendus, has said that our apparatus con- 

 tains a long wire covered with gutta percha, which being agi- 

 tated might falsify the indication. That is not correct; for the 

 communication between the conductor and the electrometer is 

 eiFected by a very short wire, not more than a metre, and which 

 is naked, having only been varnished long after it was ascertained 

 that that had no appreciable influence. 



Table III.- 



-Mean Monthly Values of the . 



Aimosph 



eric I 



Statica 





Electricity. 



Date. 



Time. 



Unit. 



1 



7 a.m. 9 



10 



Mid "l 1-35 

 day 135 



3 



5 



7 



9 



10.30 





1863. 



1 





| 















May 



6-41 7-53 





4-89' 4-57 



4-81 



4-60 5-24 



7-03 



6-91 



7-09 



August 



612 744 





5-62J 4-49 



4-72 



4-32 615 



8-10 



7-59 



696 



September ... 



4-72 5-31 





473! 417 



4-00 



5-00 5-81 



6-22 



4-44 



500 



October 



3-97 ,'3-81j 



505! 415 



3-98 



5-65j 5-29 



3-98 







615 



November ... 



4-46 | 3-85 





4-72 5-58 



4-48 



8-77 



7-85 



461 



6-70 



5-20 



December ... 



4-37 ! 7-00 





8-13 675 



6-69 



8-76 



8-79 



7-09 



610 



5-29 



1864. 



















January 



3-66 j 6-82 6-00 



713' 5-96 



6-76 



6-32 



8-30 



5-79 



4-87 



February 



2-75 3-81 4-42 



3-89 2-97 



2-56 



2-74 



519 



3-64 



5-691 



4-25 



March 



3-88 ' 3-85 



3-63 



3-321 312 



2-72 



318 517 



4-46 



April 



413 3-35 



3-491 



2-64 1 2-59 



2-78 



3-46 4-64 



403 



4-50 



It is seen by this Table that in general the electricity has a 

 double maximum and minimum, especially in summer. The 

 first maximum corresponds in the morning to 1 o'clock, the time 

 of the maximum of the current ; and it is the same with the 



