MADE IN THE UNITED STATES. 323 



XVI. Magnetic Dip at Michillimakinag Island, Michigan. Latitude 45° 51' N.; 



Longitude 84° 23' W. 

 Place of observation in the Juniper grove, on the Lake shore, about a quar- 

 ter mile south-west from the new Fort Makinag, and out of the village. 



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



1841, Sept. 12, H—H, P. M. Observed dip, Poles direct, 70° 32'.16 76° 37'.18 



" " " Poles reversed, 35 .95 31 .70 



Mean dip, 76 34 .05 76 34 .44 



Mean dip of both needles, 76 34 .24 



Remarks: — Weather, flying clouds, sun shining at intervals; brisk north-west 

 wind, increasing during the observations. The temperature during the observa- 

 tions from 70° to 75°. The sky, which was overcast during the evening, cleared 

 up about ten o'clock, at which time a beautiful aurora borealis made its appear- 

 ance, with brilliant coruscations, and remained luminous part of the night. 



XVII. Magnetic Dip at Michillimakinag Island, Michigan. 

 Place of observation west side of the ruin of old Fort Holmes, on the top of 

 the hill, about two hundred and sixty feet above the level of the Lake. 



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



1841, Sept. 13, 2i— 4, P. M. Observed dip, Poles direct, 76° 37'.10 76° 32'.05 



" " " Poles reversed, 30 .75 39 .75 



Mean dip, 76 33 .92 76 35 .90 



Mean dip of both needles, 76 34.91 



Remarks: — Weather cloudy, south-west wind, rather strong towards the 

 close of the observations. The temperature during the observations from 76° 

 to 70°. During the ensuing night the sky cleared up, and at about 11 o'clock 

 was perfectly clear, the aurora borealis, as in the preceding night, appearing 

 with great beauty. I was, unfortunately, so situated as not to be able to allow 

 my magnetic apparatus to remain in position, whereby I might have ascer- 

 tained any influence exercised by this phenomenon. 



XVIII. Magnetic Dip at Chicago, Illinois. Latitude 42° 0' N.; Longitude 87° 44' W. 

 Place of observation in a small grove, near the borders of Lake Michigan, 

 and north side of Chicago River. 



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



1841, Sept. 18, 91—111, A. M. Observed dip, Poles direct, 72° 42'.22 72° 48'.75 



" " '« Poles reversed, 49 .60 42 .80 



Mean dip, 72 45 .91 72 45 .77 



Mean dip of both needles, 72 45.84 



VIII. — 4 G 



