334 
MR. AIRY’S ACCOUNT OF THE HARTON EXPERIMENT 
small irregularities + oi' ~ affecting the ratio or multiplier of each, the sum of all 
the components will be sensibly free from the effects of these irregularities. 
53 . In like manner, if we divide the nucleus by planes parallel to the tangent at L 
or U, as shown by the dotted lines in fig. 2 (or indeed in any other way), the attrac- 
tions of the slices thus formed are additive, both in their effect on L and in their 
effect on U. Therefore, for the nucleus generally, by the same reasoning as that 
above, the effect of irregularities in the outline (and therefore the effect of the irre- 
gularities in the outline of the earth, on which these depend) will be, as I conceive, 
sensibly evanescent. But this does not apply to irregularities in the geological con- 
stitution of the earth at a small distance below L; because these irregularities, or 
rather that one irregularity, may be sensible in proportion to the whole change of 
attraction between U and L. This is a source of uncertainty from which no expe- 
riments made on the earth itself can be perfectly free. We must trust in a great 
measure to the general regularity of stratification, &c. of the district, for supporting 
us in the confidence that there is no great disturbance in the law of attractions of 
the nucleus upon the points U and L. 
54 . To illustrate in some degree the difference in the attractions and changes of 
attraction depending on different slices of a sphere, I have supposed a homogeneous 
sphere divided into twenty slices by equidistant planes parallel to the tangent at L, 
and have computed (by formulm easily investigated) the attraction of each slice upon 
the point L at the surface, and upon a point raised above the surface by^th part of 
the radius. Omitting the factor •r, the results are as follows ; — ■ 
No. of slice. 
Attraction on point 
at the surface. 
Attraction on point 
elevated Jg- radius. 
Decrease 
by the elevation of 
the point. 
1 
•17019 
•10401 
•06618 
2 
•14548 
•11404 
•03144 
3 
•12941 
•10644 
•02297 
4 
•11640 
•09811 
•01829 
5 
•10519* 
•09002 
•01517 
6 
•09515 
•08231 
•01284 
7 
•08600 
•07501 
•01099 
8 
•07756 
•06808 
•00948 
9 
•06963 
•06144 
•00819 
10 
•06217 
•05509 
•OO7O8 
11 
•05512 
•04901 
•00611 
12 
•04833 
•04315 
•00518 
13 
•04191 
•03745 
•00446 
14 
•03568 
•03207 
•00361 
15 
•02973 
•02666 
•00307 
16 
•02391 
•02161 
•00230 
17 
•01836 
•01655 
•00181 
18 
•01295 
•01165 
•00130 
19 
•00766 
•00693 
•00073 
20 
•00249 
•00232 
•00017 
* I uas not aware till I made this calculation that the plane which bisects the radius drawn to L divides the 
sphere into two segments whose attractions on L are equal. 
