A PENDULUM FOR THE REDUCTION TO A VACUUM. 
429 
Tenth set. — Results with a Brass Bar, 2 inches wide, f inch thick, and 62 inches 
long. 
31) Knife edge A. 
32) Knife edge B. 
33) Knife edge C. 
34) Knife edge D. 
Exp. 
n 
Exp. 
n 
Exp. 
n 
Exp. 
n 
142— 143 
143— 144 
154— 155 
155— 156 
2-061 
2-057 
2-054 
2-114 
145— 146 
146— 147 
157—159 
159—160 
2-071 
2-061 
2-053 
2-127 
151 — 152 
152—153 
164— 165 
165— 166 
2-098 
2-064 
2-111 
2-124 
148— 149 
149— 150 
161—162 
162—163 
2-090 
2-046 
2-104 
2-109 
Mean = 
2-071 
Mean = 
2-078 
Mean = 
2-099 
Mean = 
2-087 
If we take the mean of the two knife edges A and D (which are situated at 
the ends of the bar, and in which positions of the pendulum the heaviest weight 
is below the axis of suspension,) the value of n will be 2'079 ; and the mean 
of the other two knife edges B and C, in the reversed positions of the pendulum, 
will make n equal to 2‘088 : which two values will be the correct mean for this 
pendulum. But the difference in these values is so trifling, that the general 
mean ( n — 2'083) may be assumed for all the knife edges, without the risk of 
any material error. 
Eleventh set. — Results with a Brass Tube, 1^ inch in diameter, and 56‘2 inches 
35) Plane A. 
36) Plane C. 
37) Plane «. 
38) Plane C. 
Exp. 
n 
Exp. 
n 
Exp. 
11 
Exp. 
n 
169—170 
175—178 
2-318 
2-318 
171—172 
179—180 
2-269 
2-247 
173—174 
181—184 
2-243 
2-291 
167—168 
185—188 
2-293 
2-341 
Mean = 
2-318 
Mean = 
2-258 
Mean = 
2-267 
Mean = 
2-317 
If, as in the case of the preceding bar, we take the mean of the two planes 
A and c, which are situated at the ends of the tube, the values of n will be 
identical with each other, or 2‘318 : and the mean of the other two planes, in 
the reversed positions of the pendulum, will make n equal to 2 - 262. So that, 
with this pendulum the value of n, when the heaviest end is above the axis of 
suspension, is less than it is when the pendulum is in the reversed position : 
3 K 
MDCCCXXXII. 
