: 122 
Tasue III. 
Calculated Azimuth. | Observed Azimuth. 
36:0° 36°37° 
72:0 70°41 
108-0 103-30 
144-0 144-70 
1800 178-40 
216°0 21815 
«¢ A comparison of Table IIT. with Tables I. and I]. would 
appear to indicate, that the variable part of the hourly motion 
is due to instrumental error. 
‘¢ T may mention, in concluding this abstract, that in our 
sixth experiment, with silk fibre suspension, we obtained a 
complete revolution in azimuth of 360°. The time occupied 
in the revolution being 28" 26”.” 
[Note added in the Press, May 16, 1851.—* Before we 
commenced our experiments, and at the tine when the fore- 
going communication was made to the Academy, we had ob- 
tained a theoretical solution of the pendulum problem, founded 
on the supposition, as a first approximation, that the tension 
of the string of the pendulum was constant. The complete 
integrals obtained on this hypothesis, gave a value for the azi- 
muth, which indicated a variable angular velocity of the plane 
of vibration. This solution of the problem we have since found 
to be erroneous, and therefore believe, that the variation in 
velocity which we have observed is due to instrumental error. 
The differential equations which we made use of, and which 
contain the complete solution of the problem are the fol- 
lowing : 
