184 OBSERVATIONS OF THE MAGNETIC DIP IN THE UNITED STATES. 
Observations Repeated. 
taut | ee | Petes Bha| Mean. vine | uth, see Poles round. Betas ei 
° Uy fo} , 8 P is ; ° y ° / ° Ud 
0 |73 1.9]72 52.4) |, o on| 50\77 59.8|78 36.5 
180/73 10.4|73 a2} 13: 24 MS) 2 eos olng soa 58.2 | PSR Ed ie 
10/73 14.9/73 5.51 |5 ie5 140/76 42.0/76 56.0) le ago (| 
190|73 25.5/73 20.3 f PBR cay toy) |m BANS Bic me 352 | t 
100/87 7.2/87 a Beau eee ae 60|80 55.281 33) le) a4 
280 86 43.086 45.6 ; 240/81 31.481 357} reer 
20|74 10.1/73 any ee ae 150/75 19.3/75 172) |. 94410 
200|74 14.0/74 1.5 "Ula 7 7|| 880/75 28.4/74 30.5 | 
110 84 25.6/84 aul ee ae “i 70/84 7.2/84 0.3) lo, a9 
290/84 88/84 4.8 lS 250/84 20.984 26.6 5 ae 
30/75 22.7/74 oe “3. RR 160/74 13.674 27 Vie, a ( 
210/75 13.875 11.85 )'9 °° (1... o|| 340/74 8.5)78 40.1 | 
120/81 35.6 81 40.5 ; labora. i\\ emi || 280/86 42.086 44.0) /ae 507 
300/81 0.8/81 5.2 aes 26087 8.6.86 592 ¢ se ae 
40|76 52.4/76 352} Fe URE 17073 27.2/73 172) loa qe. 4| 
| 220/76 40.5)76 54.15 °° “°° C15 4 |) 850)73 13.5)73 58 a 
| 130|78 40.8/79 vat 78 36.941 is 
| 310/78 7.5|78 36.9 j General mean. 72° 58'.6 
These observations agree very well with the first series, but the results harmonize very 
little better with each other. If we deduct the Dip by the formula cot 6 = cot I sec a, 
we shall obtain the following results: 
First Series. Second Series. 
- AS SS = 
Azi Inclina- Inclina- 
muth. tion. Dip tion Dip. 
° 7 ° 7 ° 7 ° ? 
On. 2a T3 > QT 3) BARE SPS Qi, 
10/73 15.8]73 1.2]\73 16.38/73 1.7 
20/78 59.5738 1.3}/74 1.8)73 3.2 
80/75 5.6|72 54.8]I75 7.38/72 56.7 
40\76 45.2)72 55.1)76 45.972 55.9 
50\78 84.2|72 32.4]/78 35.1/72 33.7 
60/81 15.9\72 55.4)81 18.5)72 59.9 
70)84 14.2\78 33.7|84 15.5)73 37.1 
80\86 52.9|72 34.8]/86 53.6)72 37.7 
~iMean Dip. 72 56.7 Mean Dip. 72 58.8 
From the preceding results, it is pretty evident that the instrument with which the 
observations were made, has sustained some injury since 1844, and this injury is probably 
in the axis of the needle. The axis is apparently free from rust, and no imperfection can 
be detected by ordinary inspection, but a very slight flexure of the axis, or the smallest 
want of cylindricity, would produce discrepancies such as are here exhibited. I think, 
