= 
bs * ¥e ’ ‘ . < * 2 
“5. gee ' _* 7 
20 Magnetical Dip in the United States. 
on the face of the. published results and must be apparent by a 
coup dil to every professional observer. Why then such a la- 
bored table of them? But they all amount to nothing, literally 
they amount to nothing ; for in my mode of manipulating, adopt- 
ed since Sept. 1839, they disappear from the ‘‘ mean results ;” like 
the zero error they are mostly corrected by the reversals. I could 
_ point out what I conceive to be the cause of these vacillations, 
and the mode in which I have succeeded in merging them; but 
I have neither time nor an inclination at present, to go into details 
on these points. 1 had intended to publish the result of my ex- 
perience, but the duty to which I am here called, is very far from 
that of being an instructor of others. I certainly ought not to be 
forward in volunteering my services i in that capacity. 
The evidence which convinces me of the correctness of the 
mean results of my observations, is of the most popular kind ; a sort 
of evidence which every body can understand, equally applicable 
to moral and to physical snbjects, entirely independdlit of hypo- 
thesis and assumplions of any kind, and as ancient as the penta- 
teuch. It is simply the agreement of two independent physical — 
witnesses to the same result, under repeated and varied trials. 
. The dip is twice taken, at each place, by a mean of 16 readings of 
two separate needles. Out of 16 pairs of mean results, at differ- 
_ ent places, published in the last number of this Journal, there 
were but two, where the separate needles dis d more esi V 
of a degree. .What is common sense to infer from this? that 
there is an error of “30 minutes” in any one of. them, both the 
needles taking a fancy, or go oa to agree to the same false- 
hood. Prof. Loomis will pute the facts above stated 
and we > submit the case, whether they do not authorize the cote 
clusion which I have miei “that the results are true to within 
2or3 minutes.” nd 
Prof. Loomis has taken no notice of, this part of the evidence 
of the accuracy of the mean results of my observations. What 
must I infer from this. 7 2* : 
Lastly, Prof. Loomis cited a diadenay between the dip at 
Cincinnati, as observed by me in 1837, and the same observed 
more recently, as proof that my observations are erroneous. I 
had myself published the fact of that discrepancy, and had it un- - 
* Should the two needles each have pivots of any other fe et n that er! the c vlinder 
and be like, and alike placed in reference to the aris 7 nadie, ‘ 
an erroneous indication. But such a concurrence can remiss hap 
