DECLINOMETER. XV 
9. From the adopted values of the long and short scale divisions, the co-effi- 
cient for reducing divisions of the short scale to the same value as the divisions of 
the long scale, is — = 1-115; the reciprocal = 0-897. 
10. Determination of the scale readings at the magnetic axis of the declinome- 
ter magnet. 
For this purpose, the scale reading is first observed with the magnet in its 
usual position (direct), and next with the magnet inverted, the stirrup being made 
with prolonged sides to admit of this inversion. Simultaneous observations of the 
unifilar magnetometer are made in order to eliminate the changes of declination 
during the intervals. When these eliminations are performed, the mean of the 
reading with the magnet, direct and inverted, is the reading at the magnetic axis. 
Increasing readings (the magnet being direct), indicate decreasing westerly decli- 
nation. 
1. Observations with the Long Scale. 
May 5.1843. 1 inversal (the copper ring used) gives the zero reading, 256-87 
PMs Gs, USA GL $b) <c-n den snpnec nny -ncanoconenc-nécceennvannsarnecste-anuenuagnareesaranssnnspess 257-30 
iy 1.3 EEL STIRS OURS Ree am em Een 256:88 
Oct. 16. 1844. In the following series the copper ring was not used. 
_ TABLE 3.—Long Scale Reading at the Magnetic Axis of the Declination Magnet. 
Unifilar, minus Mean of each 
B . . 129 Se. Div. two direct, | Reading for 
Position of |Declinometer) Unifilar reduced to the |, | and of each Magnetic 
Magnet. Reading. Reading. Declinometer Direct Inverted two Axis. 
minus tt. plus u. inverted. 
Declinometer Reading. 
Sc. Div. Se. Div. . Div. Se. Div. Se. Div. Sc. Div. 
Direct 269-67 129-75 E 268-83 
Inverted. 245-10 129-58 E 245-75 268-65 
Direct 268-89 129-38 : 268-46 245-69 
Inverted 245-30 129-30 * 245-63 268-53 
Direct 269-67 129-95 . 268-61 245-62 
Inverted 243.92 130-52 : 245-61 268-69 
Direct | 271-33 131-29 . 268-78 245-57 
Inverted 242-19 132-00 . 245-53 268-72 
Direct 272-22 132-19 : 268-66 245-66 
Inverted 241-59 132-77 . 245-79 268-70 
Direct 273-31 133-10 . 268-74 
The mean reading of the long scale for the magnetic axis = 257-14. 
This determination has been adopted, as the varying position of the copper 
ring in the other series was apt to render the results uncertain. (See No. 12.) 
