recoud and results 



OF 



MAGNETIC OBSERYATIONS 



Introductory Remarks. — The present, second part, of the records and results of 

 the Arctic Expedition of 1860 and 1861, commanded by Dr. Hayes, Avill contain 

 the magnetic observations and their discussion. 



These observations wiU be given under the heads " differential observations" and 

 " absolute determinations. The former comprise a series of hourly readings of the 

 declinometer on 15 days between November, 1860, and March, 1861, at Port 

 Foidke, the winter quarters of the expedition ; also three daily readings, for the 

 same period, at stated hours. The latter class of observations includes many deter- 

 minations of the declination, the dip, and the intensity of terrestrial magnetism at 

 stations in the north of Greenland, on Smith Strait, and northward on Smith Sound. 

 The declinations were chiefly determined by means of solar bearings, but there are 

 also a few determinations with the declinometer. 



The magnetometer (or declinometer) and dip circle, and a Smalkalder azimuth 

 compass, used by the expedition, were furnished by the liberality of Prof. A. D. 

 Bache, Superintendent United States Coast Survey. Besides these instruments, 

 the expedition was provided with two small compasses and other ordinary ones ; 

 one small azimuth compass was loaned by the Bureau of Topographical Engineers. 



Description of Instruments. — The magnetometer, made by W. H. Jones, of Lon- 

 don, has an azimuth circle of six inches diameter, and can be read to 20" by means 

 of the verniers. The magnet is suspended in a box over the centre of the circle, 

 the suspension tube is eight inches long. Two magnets, each three inches long 

 and 0.3 inch in diameter, with mirror attached, are provided, also a coUimater 

 magnet 3g inches long, and but 0.3 inch of outer diameter. Ordinarily the ivory 

 scale above the eye end of the telescope is used for reading the deflections when 

 mirror magnets are suspended, for the determination of absolute declinations an 

 extra telescope can be fastened to the projecting arm of the alidade, the coUimater 

 magnet is then suspended, the glass scale of which is illuminated by a small reflector. 

 An inertia ring, thermometer, and other necessaries are also provided. The dip 

 circle was made by Patton, of Washington, new needles have been supplied by Mr. 

 Wiirdemann, they are about 8 inches in length. There are also two magnets for 

 the reversals of the poles. A three legged stand accompanied these instruments. 



10 June, 1865. ( 73 ) 



