662 Professor W. G. Adams [June 3, 



the earth, and the direction of the disturbing force seemed to be 

 constant, yet sometimes there were great differences in the deviations 

 at jDlaces not far apart, and from the result of his observations Weber 

 was led to believe that there was a centre of disturbances which was 

 somewhere in the neighbourhood of St. Petersburg. 



However sudden and unconnected single disturbances may seem 

 to be, they still follow certain laws in their occurrence ; Sabine found 

 that they had daily and yearly variations from their mean values, 

 and that they had an eleven-year period, which agreed with the 

 eleven-year period of the appearance of spots upon the sun. 



Disturbances are more frequent in summer than in winter, and 

 this applies to each hemisphere ; and it has been confirmed by 

 various observers that they are also subject to the influence of the 

 moon. Lament says of these disturbances, their cause is a force 

 which is subject to certain laws, but which does not act constantly ; 

 the mean direction and frequency have yet to be discovered. 



Observations have shown that the magnetic disturbances and 

 electric currents on the earth are so nearly related to one another, 

 that people naturally look upon the electric currents either in the 

 crust of the earth, or in the atmosphere outside it, as the cause of 

 the magnetic disturbances. These currents in the earth have usually- 

 been attributed to changes of temperature, because they also are found 

 to be in some way governed by the sun. 



Now let us come to more recent observations of magnetic dis- 

 turbances, with the improved methods of recording observations by 

 photography which are now available. For some years past photo- 

 graphic records have been taken of the magnetic elements, but the 

 curves have been laid aside, and very little use has been made of 

 them ; so much so, that some three or four years ago a circular letter 

 from Mr. Ellery, Director of the Melbourne Observatory, was sent 

 round to those scientific men who were supposed to be interested in 

 the matter, to know whether it was advisable to continue the photo- 

 graphic records of magnetic changes at Melbourne, which is the most 

 southern station, and the only station in the southern hemisphere 

 except Mauritius, where such records are taken. Mr. Ellery did not 

 for one moment suppose that they were of no value, but as no use was 

 made of them he wished to know whether the money expended might 

 not be better applied to another purpose. This matter has been 

 taken up by the Kew Committee, of which Dr. De La Eue is the 

 Chairman, and a recommendation was made that the directors of all 

 observatories which possess instruments of the Kew pattern should 

 be invited to send to Kew their photographic records, or careful 

 tracings of them, for a given period, so that a comparison might be 

 made of the results. 



The period chosen was the month of March 1879, and records for 

 the whole month have been sent from Lisbon, Coimbra, Stonyhurst, 

 Vienna, St. Petersburg, and Bombay, in the northern hemisphere, and 

 from Melbourne and the Mauritius in the southern hemisphere. 



