738 REPORT— ] 898. 



obsei'vations sliould be given ; but for many, nay, for most, purposes, 

 those who use the records will require only linal results; the means of 

 the various elements for the year, for each month, or for any other period 

 which may hereafter be adopted, and the diurnal variation, are in general 

 wanted, rather than the hourly values. If these means could be published 

 together, once a year, an enormous boon would be conferred upon mag- 

 iieticians. For special purposes the theorist will have to test his views by 

 reference to the results published in their fullest detail ; but it would be 

 no slight gain if the more salient facts could be compared by being placed 

 side by side in the same journal. One advantage such a system would 

 unquestionably possess. It would impress upon the authorities of the 

 observatories the necessity for adhering to a common form of publication. 



Some small beginnings have already been made. The Kew Observa- 

 tory Committee now publish in the ' Proceedings ' of the Royal Society the 

 annual means of the elements recorded by all the observatories which 

 send their publications to Kew. By comparing two of these tables, the 

 secular change can at once be determined. But the system is capable of 

 extension, not merely to the normal values of the elements, but to 

 disturbances. By common agreement, Greenwich and Pare St. Maur 

 publish in each year the records of the same magnetic storms. If this 

 agreement could be extended, and if the facts thus selected were brought 

 into juxtaposition, we might hope for a fuller and more instructive 

 analysis than is at present usual. 



Turning from questions of organisation, the primary business of our 

 conference will be to discuss four questions submitted to our Committee 

 by the International Meteorological Conference. 



The first two of these refer to the methods for calculating and pub- 

 lishing the monthly means of the magnetic elements which should, in our 

 opinion, be adopted. I will not anticipate the discussion which will take 

 place on these points, except to say that it will be necessary to bear in 

 mind not only what is desirable but also what is practicable in view of 

 the resources at the disposal of the directors of the various magnetic 

 observatories. 



Another question deals with the relative merits of long and short 

 magnets, and on this point we shall have the advantage of hearing a 

 report on the subject by M. Mascart. 



Lastly, there is a very important proposal for the establishment of 

 temporary magnetic observatories at certain specified places. General 

 RykatcheS" and Professor von Bezold present an excellent report on this 

 subject, and I will only remind you, that whereas the accuracy of the 

 mathematical expression of the magnetic state of the earth's surface depends 

 entirely on the number and position of the spots at which the magnetic 

 elements are accurately known, the establishment of temporary observa- 

 tories will be a costly undertaking, for the carrying out of which all the 

 resources at the disposal of international science will have to be employed. 



Another point of considerable practical importance will also be brought 

 before us. The rapid extension of electrical railways and tramways is a 

 serious menace to magnetic observatories. From all parts of the world 

 we hear of observatories ruined or threatened by the invasion of the 

 electrical engineer. Toronto and "Washington have already succumbed, 

 Potsdam, Pare St. Maur, Greenwich, and Kew are besieged, and the issue 

 largely depends upon whether these great national observatories can or 

 cannot make good their defence. 



