372 A. D. Bache on a Magnetic Survey of Pennsylvania ‘ 
Nine groups of five or six observations in each, with tigi 
were then formed. 
Recapitulation of mean (weighted) values of _— 
Group. . Latitude, — ( Lengit tude. 
L 0°39 74°83 4107 
it 39°68 77°01 41 
hae 49°22 79°99 410 
IV, 41-61 80°26 3-912 
Vs 40°68 78°14 4035 
Yr 42°89 79°00 3-618 
Vil 41°56 76°27 3-858 
i gh 8 42°85 og as bs 
EX: 42°17 74°37 3-665 
Mean, 41°34 77°45 
3-900 
aXe petal c08 ‘Lf aiLAM c cos e L-t-pdL#-+ gd? cos? L, 
‘ol long - 77 a 
Forming the conditional and normal equations we deduce: 
X=3'920 —0: 8% dL+0:0146 dM cos L+-0-0203 dLdM cos L 
01587 dL? — 0:0005 dM? cos? L. 
= i hee = ealerabls to shorten the formula and use instead 
e 
X=8-900~—0:1934 dL-++0-0134 dM cos L002 dLdM cos L. 
Comparison of observed and computed values. 
Group. x x 
P | observed. computed, ~compated. 
4°10 4:095 +0°012 
II 41 4227" —0'028 
Ur 410 4100 +0°003 
IV. 3-912 3-887 +0°025 
Vv. 4:035 4:028 +0°007 
3-618 3-651 -0'033 
IL. 3-858 3-842 +0°016 
VII 606.) 3-599 +0:007 
. | 3-665 3-670 -0°005 . 
The next and last hypothesis, 
X=8-900~—0-1934 dL+-0-0134 dM cos L, a 
in which the isodynamic lines are treated as straight lines, pre" se 
sents perhaps the best and most ome expression of the adi le 
lar distribution of the horizontal fore . 
These lines are nearly parallel with the dip lines. 
Comparison of observed and computed values on this hypothesis. 
> x | Observed | 
Group. observed. computed, —computed._ 
I 4107 4 057 +0°050 
II. 41 4216 -0'017 
41 4:143 -0°040 
IV. 3-912 3-876 +0°036 
Vi 4035 0°000 
VI. 3-618 3-616 +0°002 
VIL. 3-858 3-846 +0-012 
VU 3-606 3-605 +0-001 
Ix. 3-665 3-708 -0°043 
