52 American Association. 



faint, both with regard to the shape of the light and its motions. 

 The reasoning was this. Lightning was known to be the dis- 

 charge of electric clouds, and because the Aurora was said to be 

 like the flash of lightning, it was supposed to be discharge of 

 electric clouds in the higher strata of the atmosphere. This rest- 

 ed on very small foundations ; for instance, the same Aurora had 

 been known to be visible from the extreme point of Asia to the 

 coast of California. Electricity would not account for this. As 

 for the shape and form of the phenomena they might be account- 

 ed for by various means as well as by electricity. From the fore- 

 going considerations he was led to conclude that any argument 

 founded upon the resemblance between electricity and the Aurora 

 was inconclusive and unsatisfactory. The defenders of this hypo- 

 thesis had not agreed in anything but that the Aurora was in 

 some loay or other connected with electricity, but they disagree as 

 to the mode in which it is done. The Professor then went on to 

 discuss the various theories that had been advanced by different 

 writers upon the cause of the Aurora, and in commenting upon 

 them he begged to call attention to the real question, which was 

 this — What is the origin of the Aurora Borealis ? Is the matter 

 which composes it derived from the earth in any way, or does it 

 come down from the planetary spaces ? If the Zodiacal Light is 

 a ring round the earth and affords material for meteoric stones, 

 much more fally might it be concluded that the Aurora is ferru- 

 ginous, and tliat would help them to explain the hypothesis that 

 the Aurora is magnetic. No doubt, electricity might present 

 some of the appearances of the Aurora, but it was not suflident 

 to account for them all. The motions of the Aurora were pro- 

 gressive and not instantaneous, as was the case with electric 

 flashes. Moreover the periodicity of the Aurora was not accounted 

 for by the electric hypothesis. By another hypothesis the Aurora 

 was ascribed to magnetism. It must be admitted that there is- 

 some connection between the t^vo, as is shown in various ways,, 

 but these facts merely prove that it has magnetic qualities — they 

 prove nothing as to its origin. The material of which it is com- 

 posed and its extent, are not accounted for by any of these hypo- 

 theses, while they are satisfactorily accounted for by assigning it to 

 a cosmical origin." 



The great tides of certain bays and Estuaries are of much inte- 

 rest to the geologist, and from a paper contributed by Prof. Bache 



ON THE HEIGHT OF TIDES ON THE ATLANTIC COAST, 



it appears that the causes producing the seunusual tides are much 



