ON TERRESTRIAL MAGNETISM AND ATMOSPHERIC ELECTRICITY. 749 



and amplitude about -000012 C.G.S. unit, can at times be detected, and have been 

 shown not to be due to any peculiarities of the instrument used. They occur 

 generally between 6 a.m. and G p.m., but up to the present no direct effect of solar 

 radiation on them has been proved. In the records taken at Potsdam and at 

 Wilhelmshaven during 1895 they appear, within the limits of errors of observation, 

 simultaneously; but till more extensive observations have been made it is im- 

 possible to say how far this may be general. 



Dr. Eschenhagen also gave an account of his further work on the frequency of 

 occurrence of these small waves at Potsdam during the different hours of the day 

 and the various months of the year, and exhibited curves embodying his results. 



He considered that these waves were of sufficient importance to justify the 

 investigation of them being taken up by all observatories, and suggested that 

 similar self-registering instruments should be used at all stations, and that both 

 the north and west components should be recorded. 



5.^ Discussion on Monthly Means. 



M. Moureaux described the results of determining the monthly mean declina- 

 tion by the various methods which have been used by magneticians. The results 

 obtained differ considerably from each other, in two cases by 14 per cent. He 

 considered that two means should be calculated: tlie first by taking all days into 

 account, the second by taking only undisturbed davs. 



Messrs. Kykatcheif, Mascart, Eschenhagen, Schuster, Snellen, Eiieker, and 

 Schott took part in the discussion which ensued. 



After the discussion the following resolution was passed by the Permanent 

 Committee :—' In calculating monthly means all days are to be taken into con- 

 sideration. It is desirable to give in addition means calculated without takino- 

 disturbed davs into account.' ° 



6.' A discussion was held as to the publication of the differences 

 between the hourly means of the components of the magnetic force (X,Y,Z) 

 and the monthly means. 



After the discussion the following resolution was adopted by the Permanent 

 Committee:— 'It is desirable to publish the monthly means of the Geographical 

 Components of the Magnetic Force for each month, and also the differences 

 between the hourly means for each month and the monthly means for that month.' 



7. On Magnetic Observations in the Azores. By Albert, Prince of Monaco. 



After having perceived the capital importance of the Azores, from their 

 geographical position, for the establishment of meteorological observatories with a 

 view to weather predictions, I thought that these observatories might be of 

 service to other branches of science. For instance, the communications of Messrs. 

 Neumayer, Mascart, von Bezold and other eminent meteorologists, to the Inter- 

 national Conference of Meteorologists in 1896 show that magnetic observations 

 made at the Azores would offer the following advantages: (1) a situation near 

 latitude 40° N. (page 22). (2) Remoteness from the permanent causes of perturba- 

 tion of actual magnetic observation, such as electric lighting, tramways, and other 

 applications of electricity ; and (.3) a geographical position intermediate between 

 Europe and America, capable of furnishing most useful indications for the 

 comparison of the magnetic curves obtained in these two parts of the world 

 (pp. 36 and 90). 



The examination of these considerations and different interviews which I had 

 with M. Maacart, Director of the Bureau Centrale M6t6orologique of France 



' Question referred to the Permanent Committee by the Paris Meteorolooical 

 Conference. ° 



