proceedings: philosophical society 635 



flowed to a distance of 8 miles, indicates a basin of much larger magni- 

 tude than those at Stromboli, but still vanishing^ small when com- 

 pared with the magnitude of the earth or even with the magnitude of 

 the volcanic island (Hawaii) of which it forms a part. In fact, the 

 complete absence in the geological record, of any really great outpour- 

 ing of lava, and the absence of evidence of extreme temperatures in 

 those outlets which have been accessible to study, point to the con- 

 clusion that all are local and probably not even deep-seated phenomena. 

 Discussion. Mr. Washington called attention to the characteristics 

 of the volcanic rocks from the continent of Africa which are quite 

 different from those, for example, from Vesuvius and Etna. Mr. 

 Clarke referred to the pioneer work of Herbert Spencer regarding the 

 condition of the interior of the earth. Mr. Farquhar made inquiry 

 regarding the temperature gradients determined from borings and the 

 relation of such gradients to Chamberlin's hypothesis. Mr. Day 

 stated that, judging from the temperature gradient determined from 

 borings, the interior temperature may reach 20,000° which Chamber- 

 lin admits in his hypothesis. He stated that bore-hole temperature 

 records must alwa}^s be carefully used since conditions are generally 

 not typical; determinations of temperature gradients from different 

 sources vary by 100 per cent. 



Mr. L. A. Bauer presented a communication, illustrated by lantern 

 slides, entitled Concerning the origin of the earth's magnetic field. The 

 various recent theories regarding the origin of the Earth's magnetic 

 field were reviewed with particular reference to their bearings on the 

 general topic of the evening: the constitution of the earth's interior. 

 The hypothesis of chief interest in this connection, namely, that of an 

 iron core being the cause of terrestrial magnetism, has inherent in it 

 many difficulties, which, however, may not be insuperable. Should 

 experiments decisively show that increased pressure elevates the criti- 

 cal temperature of magnetization, then the depth of 10 to 12 miles, 

 now supposed to limit the presence of materials in the magnetic stage, 

 would be increased. However, the few experiments available indicate 

 that increased pressure lowers the critical temperature of magnetiza- 

 tion. The various hypotheses as to the earth's magnetic field being 

 caused by electric currents within the earth's crust, or as to its con- 

 nection in some manner with the speed and direction of rotation of the 

 earth, were briefly discussed. The exceedingly small effect to be 

 observed renders conclusive laboratory experiments, if not a hopeless 

 task, certainly a very difficult one with present appliances. The author 

 reiterated a belief, already expressed on a former occasion, that our 

 chief hope at present of determining the origin of the earth's magnetic 

 field appears to lie in the direction of determining what causes the 

 field to vary in the remarkable manner it does. The definite limita- 

 tions imposed by the variations in the earth's magnetic field, both of 

 the periodic and aperiodic kind, and the departures of the field from 

 the simple uniform type, are too frequently overlooked by theorists. 

 Most theories, for example, are found inadequate when the attempt is 



