4 THE VOYAGE OF H.M.S. CHALLENGER. 



tions were commenced. From this time until the final swinging for coefficients on the 2d 

 June 1876 again at Sheerness, the three magnetic elements were observed at the following 

 number of stations : 



Declination, ... 74 



Land Stations, -^ Inclination, . . . 71 



Horizontal Force, . . . 62 



Declination, . . . 25 



Stations oi swinging ship lor 



, . < Inclination, . . . 27 



Coefficients, j m . _. 



Total Force, . . . 26 



Declination, . . . 545 



Observations at sea, <( Inclination, . . . 616 



Total Force, . . . 590 



Lisbon was the first port visited after leaving England, and here the first of the 

 numerous and widely distributed series of observations were made with the instruments 

 for absolute determination. 



Accompanying the abstract of magnetical observations at land stations are descrip- 

 tive references for identifying the observation spots. The selection of these observation 

 spots was dependent on the following grounds: (1.) At established magnetic observatories 

 for instrumental comparison. (2.) At places visited by former observers, in order to 

 determine the secular change. (3.) If at unvisited sites, then -to be as free as possible 

 from local magnetic influence, and so far as could be foreseen, in a position available to 

 succeeding observers. It is a subject for regret that some of the stations adopted by 

 previous observers were at the time of the visit of the " Challenger " unapproachable from 

 the erection of buildings. 



The fixed magnetic observatories visited during the voyage were Lisbon, Cape Town, 

 and Melbourne, Australia. 



At some of the localities visited local magnetic disturbances of a marked character 

 were found to exist at spots separated sometimes only by a few feet. These places are 

 here enumerated for the guidance of future observers. Madeira, Bermuda, St. Vincent 

 (C. de Verde islands), Kerguelen island, Honolulu, Hilo, Valparaiso, Ascension. Of 

 these the Bermuda Islands are especially remarkable as having been hitherto unsuspected 

 at least for such very large local disturbances. The values of the normal Declination is 

 7t W., whereas the observations give a range of from 4 13' W. to 9 57' W. The other 

 elements also show similar anomalies, the Inclination ranging from 65 44' N. to 

 6720 / N. the Horizontal Force from 4*764 to 5'073, in a limited part of this small 

 group of Islands. 



Madeira and Ascension stand next in the order of local disturbance then St. 



