16 Magnetical Dip in the United States. 



In the paper before me, Prof. Loomis makes a distinct announce- 

 ment of the " hypothesis" in the following words : Are these 

 differences to be regarded as prrors of observation, or as errors of 

 the hypothesis of parallel^ straight, and equidistant isoclinal 

 lines ?* That is the question, which would have given a clear 

 commencement to the subject. Had the reader been advised 

 that it was upon grounds purely hypothetical, that my observa- 

 tions were pronounced in error, it was all I desired. Had Prof. 

 Loomis stopped at this point, the whole thing would have been 

 satisfactory to me ; but in the latter part of his last paper, he has 

 made a special effort to discredit my observations. I have great 

 dislike to even the appearance of controversy, especially in such 

 a journal as yours, and were it not that some instruction may 

 arise to your readers, I would suppress the following remarks. I 

 have been drawn into the subject unintentionally, by an attempt 

 to serve a friend. 



In the first place, I question the above quoted " hypothesis" it- 

 self. It is certainly anti- Baconian, to assume an hypothesis, and 

 then require observed facts to be stretched out, or cut off, by-f- 

 or — , until they agree with the assumption. We propose first to 

 consider the consistency of the hypothesis itself, as used by Prof. 

 Loomis, in his last paper, and next to reply to his special plead- 

 ings, to sustain that hypothesis, in which he endeavors to dis- 

 credit the facts observed by me. In the first group of observa- 

 tions, consisting of mine and his together, he " adopts as" a cen- 

 tral position, " lat. 41° 22', long. 84P 54V' and by the proper 

 formulae, determines " the direction of the isoclinal lines* to be 

 N. 80. P W." " Computing from these data, the dip at several 

 stations," he obtains the so called " errors of observation." Here 

 we have first the general " hypothesis," and secondly an assumed 

 " central position." 



In the second group of observations, consisting of those made 

 by myself in the region of the Mississippi, the central position 

 adopted, is " lat. 42° 00' N. long. 90° 10' W." By the formula; 

 used above, he determines the direction of the isoclinal lines in 

 this group, to be " N. 65° OP W." Again, from these data, he 

 computes the dip, and determines the so called " errors of obser- 

 vation." Agreeably to these calculations, the lines of equal dip, 



* Lines of equal dip. 



