Proceedings of the British Association. 259 



furnish a more accurate means of identification than the method now 

 in use, and at the same time give important data for ethnological in- 

 quiry. The apparatus consists of two graduated scales, each fitted 

 with a sliding gnomon. Taking the corner of the room as a con- 

 venient perpendicular, the scales are fixed against the wall at a certain 

 distance from the floor and corner of the room and at certain angles. 



Monday. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 



'Remarks on the Periodicity of Magnetic Disturbances,' by the 

 Rev. H. Lloyd. — When we examine, for the first time, the chart of 

 the changes of one of the magnetic elements during a day of distur- 

 bance, we do not hesitate to pronounce that the causes which produce 

 these changes, so apparently capricious, belong to the class which, 

 from our ignorance of their laws, we are accustomed to denominate 

 " accidental" or "irregular." Experience, however, has shown that 

 these phenomena, and therefore also the forces which produce them, 

 are subject to laws, which require multiplied observation alone for 

 their development. A few months of systematic observation is suffi- 

 cient to show that these apparently abnormal movements of the 

 magnet recur more frequently at certain hours of the day than at 

 others. Prof. Kreil seems to have been the first to notify this remark- 

 able fact. In a letter addressed to M. Kupffer, dated in January 

 1839, he observes, that " all hours of the day do not appear to be 

 equally favourable to the development of this phenomenon ;" that 

 disturbances begin " much more frequently in the evening than in 

 the morning hours, and " hardly ever begin in the latter hours of the 

 forenoon." In a letter addressed to Col. Sabine, dated in July 1840, 

 Prof. Kreil has entered more minutely into the question, with the 

 light of the observations of an additional year. He there observes, 

 that " the least disturbance takes place in the declination from 8 to 

 10 a.m., and the greatest from 8 to 10 p.m.;" that " the declination 

 is increased by the disturbances of the forenoon and middle of the 

 day, and diminished by those occurring in the evening hours ;" that 

 the effect of disturbances upon the horizontal intensity is, in general, 

 a diminution of that element, this diminution being however more 

 considerable " during the hours of the night and morning, than in 

 the forenoon and afternoon." A more elaborate examination of this 



