202 Mr. W. Ellis. On the Simultaneity of 



we cannot say. But, considering the inadequacy of our present 

 registering apparatus to ensure in all cases the necessary accuracy 

 of time indication, it becomes a question whether the coincidence may 

 not be generally closer than present means will enable us to measure. 

 To determine this with precision would, however, require some modi- 

 fication of the apparatus now in general use. 



The circumstance that the sudden magnetic movements of the 

 character here discussed appear to be so nearly, if not absolutely, 

 simultaneous over the whole earth becomes, if established, a striking 

 physical fact. In numerous cases the disturbance, commencing sud- 

 denly, and continuing for many hours, follows on a state of compara- 

 tive magnetic calm. How is the sudden change to a state of activity 

 brought about, and what is the influence that so instantaneously 

 disturbs the magnetic condition of our globe ? The magnetic move- 

 ments at Greenwich at such times are always accompanied by corre- 

 sponding earth currents, which, similarly following a state of calm, 

 become at once active, precisely at the commencement of the magnetic 

 disturbance. It is believed that a similar effect is produced at other 

 places, and that this is so is, in some cases, specially mentioned. 

 Some sudden action, apparently from without, sets up, as it seems, 

 both earth current and magnetic activity simultaneously, or nearly so, 

 over the whole earth. It is to be noted that magnetic and earth 

 current disturbance at Greenwich is, on the whole, more frequent in 

 spring and autumn, when, in its diurnal revolution, the whole surface, 

 or nearly the whole surface, of the earth becomes, during each twenty- 

 four hours, exposed to the sun, as though the earth in some way con- 

 tributed to the production of the phenomena observed, a given ex- 

 ternal influence appearing- to cause at these times a greater activity 

 than at other parts of the year. For magnetic disturbance rises 

 and falls generally with the existence of more or fewer sun spots, 

 in which variation we do not expect to find an annual period. 

 Without, however, discussing further the production of, or relation 

 between, magnetic disturbances and earth currents, on which some- 

 thing will be said in a later part of this paper, we will proceed 

 to offer some particulars more nearly concerning what has gone 

 before. 



In asking for corresponding times of magnetic movement at th& 

 places mentioned in Table I, request was also in each case made 

 for information on the- direction and character of the magnetic 

 movement, and many interesting particulars were thus supplied. It 

 is not proposed on the present occasion to treat these details nu- 

 merically, but rather to group them in such a way as to show, in a 

 simple and ready manner, the direction of the magnetic movements 

 at each place on the several days. The results are given in Table 

 III, in which the sign' -f indicates that the north end of the declina- 



