NOTES. 



409 



eclipses a small portion of the earth's surface at e, and sometimes falls 

 short of it. To a person at e, in the center of the shadow, the eclipse 

 may be total or annular; to a person not in the center of the shadow, a 

 part of the sun will be eclipsed ; and to one at the edge of the shadow 

 there will be no eclipse at all. The spaces P b E, P' a E are the pen- 

 umbra. 



Fisr. 29. 



NOTE 115, p. 42. From the extremities, <J-c. 

 If the length of the line a b, fig. 29, be meas- 

 ured, in feet or fathoms, the angles S b a, 

 Sab, can be measured, and then the angle 

 oS b is known, whence the length of the line 

 S C may be computed, a S b is the parallax 

 of the object S, and it is clear that the greater 

 the distance of 8, the less the base a b will 

 appear, because the angle a S' b is less than 

 a 3 ft. 



NOTE 116, p. 43. Every particle will describe a circle, Src. If N S, fig. 

 3, be the axis about which the body revolves, then particles at B, Q, 

 &c., will whirl in the circles B G A a, <J E qd, whose centers are in the 

 axis N S, and their planes parallel to one another. They are, in fact, 

 parallels of latitude, Q. E q d being the equator. 



NOTK 117, p. 43. The force of gravity, &c. Gravity at the equator 

 acts in the direction d C, fig. 30 ; whereas the direction of the centrifugal 

 Fiff.30. 



MM 



