508 L. A. Bauer — Wilde on Terrestrial Magnetism. 



As this paper might be considered incomplete were no refer- 

 ence made to one or two things which have been brought 

 forward as verifications, I will briefly allude to them. Wilde's 

 next strongest argument to those given above, is a table which 

 gives the westerly progression of the zeros of declination 

 across the Atlantic from 1492-1880, and herein is included 

 that very ancient observation of Columbus where his needle 

 changed from east to west, concerning the exact location of 

 which there has been controversy. All that will be said is 

 that Wilde gives no means for the verification of his figures, 

 as he did at those stations which have been discussed. Fur- 

 thermore the table has been obtained on the assumption that 

 the inner sphere retreated at the annual rate of 22*5 minutes 

 of arc. It has already been shown that for St. Helena the 

 sphere lagged behind 27 /- 8 and the table of periods shows that 

 for every point on the globe this rate is different. Again, the 

 points mentioned affecting the accuracy of a determination of 

 the declination on the Magnetarium and from comparisons 

 made between fact and theory wherever possible, it is very 

 much doubted if Wilde can get within 5° — certainly not within 

 3°. Now when you take into consideration that if the isogonic 

 lines do not cut the meridians or parallels sharply, it can be 

 seen how little reliance can be put upon the determination 

 of geographical position by means of the magnetic declina- 

 tion. Nor need Wilde have gone back to the time of Colum- 

 bus, where we have absolutely no data, to verify his theory. 

 If he will reproduce in range and period, Paris, Cape of Good 

 Hope, New York City, and St. Johns, conjointly not sepa- 

 rately, we will ask no further verification. 



The opinion of this paper then is that while Wilde's theory 

 has given us a secular variation, it has not given us the secular 

 variation as manifested on the earth. Nor has it given us a 

 better representation than the old theory of a uniformly re- 

 volving magnetic pole. Furthermore, have we not taken a 

 step backward ? If we go back to Halley, two centuries ago, 

 we find the idea embodied in Wilde's mechanism, expressed in 

 all detail and without any difference worth mentioning. A 

 full description of Halley's theory* can be found in Harris' 

 Rudimentary Magnetism. We are obliged then to charac- 

 terize the Magnetarium as nothing more than an improved 

 Barlow globe, and in conclusion we will say with Halley that 

 the " secular period and motion are secrets as yet utterly 

 unknown to mankind, and reserved for the industry of future 

 ages." 



* Originally given in Philosophical Transactions of the Royal Society for 1683, 

 p. 208 and for 1692, p. 563. 



