qr. 
119 
steel plate, this being mounted as in the preceding experi- 
ments. Our observations were taken, during the earlier ex- 
periments, at intervals of five minutes, which we afterwards 
changed to ten minutes ; and having thus determined the im- 
portant points, we watched these continuously, using an interval 
of twenty minutes for the other portions of the motion. 
‘s The two experiments with hemp fibres occupied a time 
exceeding sixteen hours each. The experiments with the 
wire suspension occupied periods of twenty hours each, and 
the experiments with the silk fibre suspension occupied fifteen 
and nineteen hours respectively. At the close of these periods 
the motion was distinctly visible, and being almost rectili- 
near, the direction of vibration could be determined with con- 
siderable accuracy. 
‘“‘ The results of these and subsequent experiments will 
shortly be offered to the Academy in detail; at present we 
shall confine ourselves to an abstract of those results, and 
to a brief comparison of the theory of M. Foucault with obser- 
vation. 
‘‘ The facts which we observed, without making any allow- 
ance for instrumental error, apsidal motion due to the dif- 
ference between the arc of vibration and its sine, or disturb- 
ances produced by the air, may be expressed by the following 
statements, the initial motion being in the meridian : 
*©JT. The azimuthal velocity diminished from the com- 
mencement of the motion, attaining a minimum in the position 
between E. 30° N. and E. 
“TI. The azimuthal velocity increased after it had passed 
the east, and attained amaximum, which appeared to lie between 
S. 40° E. and S$. 
‘¢ TIT. The motion of the azimuthal plane near the south and 
south-west appeared very unsteady, as if greatly affected by 
disturbing causes; but indicated a general tendency to increase 
its rate from S. to S. W. 
