18 Magnetical Dip in the United States. 



lines marked by the Architect of the Universe. My observations 

 were intended to be tried by no other standard than the last. 



I come next to Prof. Loomis's remarks against the truth of my 

 observations. 



On page 88, he doubts whether I have attended to reading 

 both ends of the dipping needle, so as to avoid the error " arising 

 from the eccentricity of the axis of the needle in relation to the 

 vertical circle, on which the readings are made." He says, " this 

 error in my instrument, commonly amounts to one or two min- 

 utes, and sometimes to even five or more. It is corrected by 

 reading at both extremities of the needle." From my saying 

 that I determined the dip by 8 distinct readings, he thinks I " im- 

 plied that I did not attend to the above precaution." This is all 

 naivete enough. I regret that Prof. Loomis should have formed 

 so low an estimate of my skill, as to suppose I would use a grad- 

 uated circle, where it was possible to obtain the mean of two op- 

 posite readings without doing so, — a thing so obvious that I 

 deemed it unnecessary to say any thing about it. My needle 

 No. 1, when properly adjusted, shows no eccentricity, but reads 

 alike at both extremities. No. 2, has almost uniformly a differ- 

 ence of 5 minutes at the opposite ends. Both ends of both nee- 

 dles were always observed. If such be called a separate reading, 

 then 16 should be substituted for 8 in the quotation above, and 

 my readings should all be counted double the number which I 

 have assigned to them. 



The next paragraph is upon " the uncertainty of the readings 

 themselves." I should not have known how to reply to that 

 expression, but he subsequently becomes more specific. " The 

 error arising from friction on the axis," he says, "is exhibited in 

 Prof. Locke's observations in a striking lightJ^ I find by the 

 subsequent remarks that he refers to an observation at Davenport, 

 as published in Vol. xxxix, of this Journal, in which there was 

 an erratum, which had been ^the subject of correspondence be- 

 tween the Junior editor and myself. This erratum was the re- 

 sult of transcription. The amount of the several items, was cor- 

 rectly written, but one of the items which in the field-book reads 

 72° 55' had been transcribed 72° 05^ The Junior editor dis- 

 covered the discrepancy between the items and their amount, and 

 very naturally corrected the latter instead of the former, at the 

 same time kindly addressing a note to me on the subject, which, 

 as I was absent, I did not receive. It went to press in the erro- 



