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 errors 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 
Fi 
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-+ — 
until they agree with the assumption. We propose first to 
er the consistency of the hypothesis itself, as used by Prof. 
© eredit 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. 84° 54’,” and by the proper 
3 mule, determines “ the. direction of the isoclinal lines* to be 
N. 80.1’ W.”. “ Computing from these data, the dip at several 
tations,” he obtains the so called “ errors of observation.” Here 
we have first the eevee ‘‘ 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 
7 is “lat. 42° 00’ N. long. 90° 10’ W.” By the formule 
__ used above, he determines direction of the isoclinal lines in 
* this group, to be “ N. 65° Ol 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. 
& et 
ie ge 
ais, in his last paper, and next to reply to his special plead- _ 
ings, to sustain that hypothesis, in which he endeavors to dis- — 
