280 



RECREATIVE SCIENCE. 



" cone of slaadow" must engage our tliouglits 

 for a few minutes — the cone of darkness 

 (turned exactly away from the sun), which 

 evermore accompanies the earth, and which 

 the moon occasionally enters, either com- 

 pletely or in part, when her varying path 

 conducts her sufficiently near to being in a 

 straight line with the earth and sun. 



Fio. 1. 



Fig. 1 represents the leading circumstances 

 connected with the shadow; its conical shape 

 is due to the superior size of the sun as com- 

 pared with the earth. When a large lumi- 

 nous body (for instance, the sun) illuminates 

 a small opaque one (as the earth), the latter 

 must cast a conical shadow. The round form 

 of the section of this cone, as viewed when its 

 rim is projected on the moon during the pro- 

 gress of an eclipse (see Figs. 2, 3, and 4), is a 

 visible demonstration of the earth's round 

 shape. It is a portion of the earth's silhouette. 

 To return to the figure : E represents the 



Fig. 2. — Ih. 5Sin., Green-wicla time. 



earth, one side basking in sunshine, the other 

 casting the usual conical shadow, in which the 

 moon, M, has entered centrally, thus under- 

 going total eclipse. The faintly shaded por- 

 tion, a a, represents the region adjoining the 

 shadow, from which a portion of the sun's 

 disc is hidden by the earth's body, thereby 



causing a partial shadow, or "penumbra." 

 The moon always travels a considerable time 

 through the penumbra before passing into 

 the true shadow. 



So far this explanation corresponds with 

 that contained in all works on astronomy ; 

 but we now come to the consideration of some 

 circumstances due to the presence of the 



Fig. 3. — 2h. 20m., Greenwich time. 



earth's atmosphere. JSTot the portion of 

 atmosphere which intervenes between our- 

 selves and the eclipsed moon, but that por- 

 tion which surrounds this great earth's outline, 

 as viewed from the moon. Imagine a special 

 ray from the sun, d, e, passing through the 

 atmosphere to the surface of the earth ; the 



Fig. 4. — 21i. 50m., Greemvich time. 



presence of that atmosphere will alter its 

 direction — will malce it hend, as you have seen 

 an oar appear to do when plunged obliquely 

 in water. On proceeding from e, through 

 the remainder of the atmosphere, the ray 

 becomes additionally bent, and in the game 

 direction; the consequence is, that it will 



