66 KEPORT — 1 886. 



Bolar-diurnal variations of tlie three magnetic elements which ought, in his 

 opinion, to hold on the hypothesis that these variations are caused by cur- 

 rents in the upper atmospheric regions. One of these is that the horizontal 

 force component of the daily variation ought to have a maximum or mini- 

 mum at the time when the declination component vanishes — that is to say, 

 attains its mean position. Another is that the horizontal force ought to 

 be a maximum in the morning and a minimum "in the afternoon in the 

 equatorial regions, while in latitudes above 45° the minimum ought to 

 take place in the moi'ning. A third is that in the equatoi'ial regions the 

 maximum of horizontal force ought to be coincident with the minimum 

 of vertical force, and vice versa. 



These conclusions are considered by Dr. Schuster to be sufficiently 

 well confirmed by observations, and thus to render hopeful the first 

 attempt to apply the Gaussian analysis to the solar-diurnal valuation. 



The appendices of Captain Creak (I.) and of Dr. Schuster (VII.) have 

 reference to this subject, and maintain the importance of some action 

 being taken by the Committee to prepare for a thorough application of 

 the Gaussian analysis to the magnetic variations. It will be seen fi-om the 

 remarks of Dr. Schuster that some time must elapse before observations 

 are obtained sufficiently good and complete to justify a systematic appli- 

 cation to them of mathematical analysis. This circumstance has induced 

 the Secretary- to lay before this Committee in Appendix VIII. a pro- 

 visional working hypothesis I'egarding the cause of the periodic variations 

 of terrestrial magnetism which has gradually gi'owu up by contributions 

 from various quarters. 



While this Committee do not hold themselves responsible for the 

 various statements contained in this hypothesis, they would point out the 

 desirability of ascertaining to what extent well-known magneto-electric 

 laws may succeed in accounting for the phenomena of terrestrial magnet- 

 ism, and likewise the desirability of ascertaining to what extent the 

 magnetic earth appeal's to be subject to the laws of ordinary magnets. 



A preliminary working hypothesis of this nature might serve to elicit 

 facts while the material for the Gaussian analysis is being completed, and 

 it would add to the interest of the final result if we should obtain reason 

 to think that electric currents in the ui^per atmospheric regions are at 

 once the iraiaediate ratises of magnetic variations and the effects of atmo- 

 spheric motions in these regions, so that a knowledge of the one set of 

 currents might possibly enable us to determine the other. 



In Ajipendix IX. we have a practical example by Mr. C. Chambers of 

 the method of reduction which he suggested in Appendix XII. of the last 

 report of this Committee. Finally, in Appendix X. there are some remarks 

 by Captain Creak on the advantages to the science of terrestrial magnet- 

 ism to be obtained from an expedition to the region within the Antarctic 

 Circle. 



The Committee have drawn 10?. 10-^., and returned to the Association 

 a balance of 291. 10s. They would desire their reappointment, and would 

 request that the sum of 501. should be placed at their disposal, to be spent 

 as they may think best on the researches mentioned in this report. 



