27 



axes," and " that the line of no variation is a great circle of the 

 earth, and is that magnetic meridian which, after cutting the 

 magnetic pole, passes at the distance of 6° 28' from the pole of 

 the earth," — Dr. Patterson remarked that these notions were 

 directly contradicted by well observed facts, that there are more 

 than two magnetic poles, that the magnetic poles are not in the 

 polar circles, that there are several lines of no variation, and 

 that those lines are not great circles, but are altogether irregu- 

 lar in their course. 



4. The practical applications of Dr. Sherwood's theory are 

 announced in these terms: "With the correct dip given him, 

 observed at a given time, he works out either or all of the fol- 

 lowing results: the variation of the needle, the distance of the 

 circle of no variation from the place, and its angle with the 

 meridian, and the latitude and the longitude. With the va- 

 riation given him, in the same manner, he determines the 

 dip and the other results. He must know, however, if the 

 dip be given, whether the place of observation is east or west 

 of the circle of no variation; and if the variation be given, 

 whether it is north or south of the magnetic equator, and near 

 the arctic or antarctic semicircle of no variation." 



It is sufficient to remark, said Dr. Patterson, on this train of 

 assertions, that they necessarily assume the truth, within the 

 limits which are stated, of two positions; 1st, that the same dip 

 will always correspond with the same variation, and 2d, that 

 every place on the earth's surface has a different dip from all 

 others, — both of which are notoriously untrue. The various 

 examples, contained in the Report, of calculations made from 

 the single datum of the dip or the variation, and which give for 

 results all the other particulars with an accuracy extending not 

 to seconds merely, but to thirds, must be regarded as illusory. 



Mr. Walker also made a verbal communication on the sub- 

 ject of Dr. Sherwood's alleged discoveries. He remarked that 

 even admitting the correctness of the Doctor's hypothesis, as 

 stated in his Memorial to Congress, still his method would be 

 of no use for nautical or geographical purposes, for the follow- 

 ing reasons: — 



1. The apparatus for determining the dip and variation of 



