288 ON EAETH CURRENTS, AND THE DIURNAL 



a calculation, similar to the foregoing, for places at which hourly, 

 or two-hourly, observations of the two magnetic elements have 

 been made for any considerable period. The results of these- 

 calculations are given in the following Tables. 



Table YI. contains the names of the places, together with their 

 geographical co-ordinates, and magnetic elements, the positive sign 

 denoting north latitude, east longitude, and easterly declination. 

 The years in the sixth column of the Table are those of the hourly 

 observations which have been employed in the calculation. The 

 absolute values of the magnetic declination and intensity, in the 

 fourth and fifth columns, correspond to the mean time of the period. 

 The observations were taken, in all cases, at the full hours of 

 Gottingen mean time ; but the corresponding local time is indicated 

 in the last column of the Table, the numbers being the minutes to 

 be added to, or subtracted from, the Tabular hours. 



Tables VII. and VIII. contain the calculated values of the 

 azimuth and intensity of the current, at the several hours of obser- 

 vation, for each of the foregoing stations.* 



* The diurnal changes of declination and horizontal intensity, employed in the cal- 

 culation, are contained in the following works : 



1. " Magnetical and Meteorological Observations made at the Royal Observatory, 

 Greenwich (1844-47)." 



2. " General Results of the Makerstoun Observations." Edin. Trans., vol. ix. 



3. "Resultate des Magnetischen Observatoriums in 'M.vnchen."Abhandh<ycH 

 der K. Akademie der Wissenschaften, Miinchen, band v. 



4. "Resultate aus den Magnetischen Beobachtungen zu ~Pro.s"Denkschriften 

 der Eaiserlichen Akademie, Wien, band viii. 



5. " Annales de 1'Observatoire Physique Centrale de Russie (1850-55)." 



6. " Observations made at the Magnetical and Meteorological Observatories at 

 Toronto, Hobarton, St. Helena, and the Cape of Good Hope." 



7. " Magnetic and Meteorological Observations made at the Girard College, Phi- 

 ladelphia." 



