MADE IN THE UNITED STATES. 325 



lar atmospheric changes, I moved the instrument to a ravine in the bluff, about 

 one hundred yards north of the former station, and there I observed the needle 

 No. 2. 



The next morning I repeated the observations of both needles at the station 

 of the needle No. 2, of this day, as will be seen in the following records. 



XXII. Magnetic Dip at Peru, Illinois. 

 Place of observation in a ravine about eighty yards from the lower end of 

 the town, and about one hundred yards north of the Illinois River, the same 

 station as occupied yesterday for needle No. 2. 



Date. Hour. Needle No. 1. Needle No. 2. 



1841, Oct. 1, 9i— lU, A, M. Observed dip, Poles direct, 71° 45'.70 71° 53'.30 



" " " Poles reversed, 53 .23 44 .55 



Mean dip, 71 49 .46 71 48 .92 



Mean dip of both needles, 71 49 .19 



Note. — The last three stations at Juliet, Ottawa, and Peru, whose latitudes differ but little, 

 especially the last two named, yield, according to my observations, magnetic dips, which, as they 

 are not justified by differences in longitude, so neither can they be accounted for on the supposition 

 of any local attraction, as there are no indications of the occurrence of iron ore in the vicinity, the soil 

 containing but the usual trifling proportion of oxide of iron belonging to nearly all regions, the in- 

 fluence of which is considered as inappreciable by our instruments. On the other hand, I have no 

 reason to doubt the accuracy, within the usual limits, of my own observations, as they were made 

 with a tried instrument, and with all the care of which I am capable. As, so far as I know, the 

 true geographical position of these three places, has not been astronomically determined, it is pos- 

 sible that when this shall be done, there will be found more conformity in the relation existing be- 

 tween the difference of geographical position and that of the magnetic inclination. In reference 

 to that subject, I have much regretted not to have been able to determine the position of these 

 three places; the haste of my journey as well as the inclemency of the weather having prevented 

 me, excepting at Ottawa. At all events, should any error have been made in determining the 

 magnetic dip at any of these three stations, it cannot have happened at Peru, the result there 

 having been confirmed during two consecutive days of observations. This error may arise from 

 a repeated mistake in reading off the degrees of the two needles, which, though I cannot realize it 

 to myself, is nevertheless possible, since, as at Ottawa, the different positions in which the needle 

 is placed during a complete observation indicate degrees of different denominations. We should 

 guard, however, against any preconceived notions in reference to phenomena so delicate and com- 

 plicated as those relating to the laws that regulate the distribution of magnetism over the surface 

 of the earth, and which are yet so little known to us. 



The foregoing observations, therefore, are submitted for as much as they are worth for the pre- 

 sent, in the hope that some future observer at Juliet, and Ottawa, will take the trouble to confirm 

 or refute them. 



