Dip and Variation of the Magnetic Needle. 101 
Adopting for the central position, lat. 41° 18’ N., lon. 81° 12/ 
wwe we obtain the usual equations, which farnish us }=1.96851, 
pein, 01483, y= +.00378, and the direction of the isoclinal line 
is aie N. 75° 42’ W. to S. 75° 42’ E. The increase of dip in the 
normal direction is 55’.081 to sixty geographical miles. Comput- 
ing from these data the dip at the several stations, we obtain the 
differences given in the last column above. | Two of these differ- 
ences exceed ten minutes, viz. at Cleveland and Hebron. Ihave 
observed the dip near Cleveland four times, on different sides of 
the city, with the following results: 
. May 9, 1839, on the north side ad rig city, 73° 26/.0 
Sept. 22, 1840, “ south 12.0 
April 23, 1841, “ west 5 16.3 
Aug. 12,1841, “ east " 4.3 
“The Ssduinet dip is the mean of these réiie observations, and 
as the computed dip is almost identical with one of the obsertae 
tions, itcannot be pronounced inadmissible. At Hebron, obser- 
vations were made at two stations, distant about ten rods from 
each other, with sensibly the same result. As however at Fra- 
sersburgh, distant but about twenty miles, the computed dip agrees 
well with the observed, we may presume that this disturbance is 
quite limited in extent. 
Classifying the differences in the same manner as with table I, 
the mean at ne twelve northern stations is — 1.5; at the twelve 
southern +145 at the six most eastern — 0/9; at the si a 
western 03: at the twelve one} +06. GEN 
i 
ius 
. 1 is a a re : ~22 
3/1841. Aug. 31} « *T= 1.6 
21840 June 30, # “142 
4/1840. June 30) « =—7 2 
1840. June 30) «— +170 
.1|1839. May 17} x + 9. 
.11839. May WW * < ea 
1840. Aug. Prof. Locke, nats 
11833. March30| “ 2g - 0.3 
Jan. 4) Profs. Locke and Loomis, —19 .3 
1833, March 29 Prof. Locke, + £8 
839. Jun eae i 
1840. en 94 “ 4 +49 
. Ang. 20) * a +e 3.0 
1940. Aug. 29 ma 
