92 



RECORD AND RESULTS OF 



MAGNETIC INTENSITIES. 

 Observations and Results. 



Washington, D. C, June, 1862. 

 The following observations Avere made by myself at Washington, D. C, for the 

 purpose of determining certain instrumental constants required for the reduction 

 of the intensity observations made by the expedition. 



The instrument was received here in May, 1862; it had not been used since its 

 return from Greenland. 



Determination of Moment of Inertia of Ring G. 



Dimensions: Outer diameter, 2.335 inches) rn l m^ -n ^ 



' V Temperature, 81° Fah. 



Inner " 1.812 " j ' 



Weight, 512.62 grains 



Moment of inertia K^ =^ | (r^ + r^"^) lo. Where r and Ti (in feet) equal outer 

 and inner radius and lo the weight, we find 



log ^, =0.63171 at 81° Fah. 



log ^1 =0.63775 at 85 " 



the linear expansion being 0.0000105 parts for each degree; the thickness of the 

 ring is 0.147 inch; it is of bronze. 



Determination of Moment of Inertia of Magnet Z 6 and its Ajij^endages. 



Station, Coast Survey Office, Washington, D. C, June 13, 1862. Determination of value of one 



division of scale on telescope. 



Forming the differences we have 

 17° 22' 45" = 1028.8 divisions or 

 1 division = 1'.014 



The azimuth circle reads in the direction from S. towards W., and an increase of 

 scale reading (on telescope) corresponds to an east movement of the north end 

 of the magnet. 



Change of magnetic moment of deflecting magnet (Z 6) for 1° of temperature, 

 5=0.0002. 





Azimuth circle. 





Scale divisions. 



5° 11' 



20" 



18' 



20" 



300.8 



295.2 



9 16 



20 



11 



00 



59.5 



64.1 



33 



40 



34 



40 



519.0 



575.5 



5 15 



10 



16 



00 



301.7 



298.4 



Experiments of Vibration. 



Set 1. 



Magnet Z G suspended. 



Chronometer Kessels 1241, fast of mean time 2'' 32", gains daily 6", 

 Charles A. Schott, observer. 



No. of vibrations. 



Time. 







2" 31™ 



49^0 



20 



38 



57.7 



40 



40 



06.6 



60 



41 



16.1 



. 80 



42 



24.7 



100 



43 



33.6 



200 



49 



18.9 



300 



55 



03.7 



320 



56 



12.6 



340 



51 



22.0 



360 



58 



31.0 



380 



50 



40.1 



400 



3 00 



49.1 



Temperature. 

 85° Fah 



83.0 



Extreme scale readings. 

 359 and 241 



319 and 277 



300 vib'ns at 84°.0. 



Mean 



17" 14".7 

 14.9 

 15.4 

 14.9 

 15.4 

 15.5 



17 15.13 



