450 



EXPEDITION TO POINT BAKKOW, ALASKA. 



\ rtrtiea.1, -firci. in Aarijufi 



force iiiaguc'tometcr, to be relatively disposed of in a building' as shown in the accompanying dia- 

 gram. The size of the observatory was to be 3 by 5 meters, or about 10 feet by 1CA feet inside, and 

 Gi to 7 feet high ; size of the brick piers, 0.3 meter square and about 1 meter high : cross-section of 

 telescope pier, 0.15 meter by 0.6 meter long, and of the same height as the instrument piers; tho 

 brass cylindrical vessels in the axis of which the magnets are suspended, except the knife-edgo of 

 the Lloyd balance which passes through the center, are each of 40 centimeters diameter. Tin's 

 new observatory should be distant from the older one at least 8 meters." 



The following notes were prepared for the guidance of the party, May 31, 1882: 

 Xotes on the mounting, the adjustment, and the determination of instrumental constants of 

 the I. rook e differential magnetometers: 



"1. THE DECLINOSIETER OK UNIFILAE MAGNETOMETER. 



"Take out the torsion of the suspension skein or wire suspending alternately magnet and 

 Aveight until the telescope readings are the same; adjust fixed mirror to read 50 of scale (which is 

 to be recorded as 500); adjust movable mirror to read the same for average position between daily 

 extremes; note reading t of torsion circle. Measure torsion of suspension by turning ofl',J degrees 

 to right and to left and reading the scale (through telescope); turn torsion circle back to reading t. 



"Let /= length of a division of scale, r = radius or distance from face of scale to surface of 

 mirror (if of glass, silvered on back, ?, of the thickness of the glass must be added); then the 

 angular value of one division of scale 



= 3437/75 ' 

 '_'/ 



"For the magnetometers the value of / is uniformly 1 millimeter, and the angular value. = 1'. 

 the radius r being = 1.719 meter, which has to be carefully measured oft' for each instrument. 



