The elements of astronomy; a textbook . Fig. 123. Explanation of the FoucaultPendulum 366 APPENDIX. [§ 494 The total amount of this deviation in a day is easily estimated geo-metrically. Suppose a parallel of latitude drawn through the placewhere the experiment is made, and a series of tangents drawn atpoints close together on this parallel. Allthese tangents will meet at some point V(Fig. 123) which is on the earths axis pro-duced, and taken together they form a conewith its point at V. Now if we supposethis cone cut down on one side and openedup (technically, developed ), it wou
The elements of astronomy; a textbook . Fig. 123. Explanation of the FoucaultPendulum 366 APPENDIX. [§ 494 The total amount of this deviation in a day is easily estimated geo-metrically. Suppose a parallel of latitude drawn through the placewhere the experiment is made, and a series of tangents drawn atpoints close together on this parallel. Allthese tangents will meet at some point V(Fig. 123) which is on the earths axis pro-duced, and taken together they form a conewith its point at V. Now if we supposethis cone cut down on one side and openedup (technically, developed ), it would giveus a sector of a circle, as in Fig. 124,and the angle of the sector — the unshadedangle AVA of Fig. 124—would be theB sum total of the angles between all the Fig. 124.—Developed Cone, tangent lines of which the cone is com-posed. It is easy to prove that ABA =360° X sin lat. (see General Astronomy ). In the northern hemisphere the plane of vibration of theFoucault pendulum moves round with the hands of a watch;in the southern, the motion is reversed. 495. Determination of Azimut
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