XXII 



INTRODUCTION. 



At the termination of the preceding, a second series of vibration experiments completes the 

 data required for a single determination. The routine of observation will appear more clearly 

 in the following transcripts from the note-books. 



WASHINGTON, MAY 20, 1854. 



The radius of the vibration apparatus and unifilar magnetomer, including two-thirds the 

 thickness of the plate-glass mirrors, was found to be 1.414 foot, the divisions measuring 



From 100 to 300 

 200 to 300 

 300 to 400 

 300 to 500 



Foot. 



0.166 

 0.083 

 0.083 

 0.166 



Value of 1 div. 

 do. 

 do. 

 do. 



Foot. 



0.00083 

 0.00083 

 0.00083 

 0.00083 



Resulting arc value of 1 division, 1'. 00896. 



Experiments were next made for the moment of inertia of the deflecting magnet. The base 

 of the vibration apparatus (in the office) being levelled carefully by means of the plummet, it 

 was suffered to stand until the latter ceased rotating, when magnet No. 5 W was suspended and 

 raised to proper height for vision of the ivory scale reflected into the telescope. The table-top 

 was then turned in azimuth until the vibrations of the magnet were equal on each side of the 

 central scale division, and was clamped in that position. When the magnet had come to rest, 

 the torsion circle was turned alternately through 90 in each direction, and the corresponding 

 scale readings noted as in the subjoined table. 



Observations for the value of -** ivitliout weights. 



22'.335 



.___ 

 F ~~ w u ~ 10800' 22'. 335 



in .002054. 



Careful measurement of weight No. 14 showed its diameters to be r 3.60iVi., r 1 ' =. 3.03tti., 

 and weight W= 1100 troy grains. Facilitated by a disc of wood, having a groove in which 



