90 P. E. Chase on Mechanical Polarity. 
subdivision again into Cape St. Lucas, and the latter into 
Florida. Northward the eastern province extends more and 
more westward reaching the Rocky mountains and even west 
ward of them towards the Yukon 
The southern boundary of the middle province of North 
America may be arbitrarily established as a straight line, drawn 
from the mouth of the Rio Grande to that of the Yaqui near 
Guaymas on the Gulf of California, thus ae into North 
America the whole of Florida and Lower California, 
[To be continued.] 
Art. XIII. —Bperiment on Mechanical Polarity * by PLINY 
LE Cuase. M.A., S.P.A.S. 
{Continued from vol. xl, p. 316.] 
C. AppaRAtus-PoLariry. 
Friction and the jarring of the apparatus, modified by the 
degree of velocity imparted to the ring, produce a colerity of 
their own which should be carefully estimated, and due allow- 
ance made for its influence in all delicate and doubtful a 
ments. In order to determine the directivity of the normal vi- 
eect independent of any mere current influence, the ne 
shielded ty a — as in the ordinary surveyor’s or marin- 
a's $ compass. 
27. ‘When the axis is in the meridian, the polarity appears to 
be meridional. 
bach With the axis in the equator, the polarity is also me- 
ridion 
29. 7 the northern extremity oo the axis is inclined to the 
west, the needle declines to the eas 
30. Giving the axis an easterly santanaibe, the needle declines 
to the em The declination is, therefore, from the axis in all 
cases, and we may infer that the earth’s rotation exerts a con- 
stant endanee to increase the normal declination of the needle. 
81. In all positions of the axis there appears to be a slight 
disposition in the needle to decline to the east, independent of 
the motion produced by the mere vibration of the apparatus. 
If this disposition is owin g to terrestial currents, it is probable 
that the declination would be westward in the southern hemi- 
° a force 
recat from the earth’s rotation which deflects tt to the right in the — 
rthern i but to the left in the pain pe fog 
eanisk 07.) 
1 From the ae of the American Philosopbical Society, vol. x, pp. sib Ti 
