478 PHYSICAL SCIENCES. 



the centre, where they run together in a blaze. The more condensed part 

 is projected on a ground of irregularly scattered stars, which fills the whole 

 field of the telescope. There are few stars near this cluster. 



NOTE 236, p. 420. Plate 8 shows five nebulae as seen in Sir John 

 Herschel's 20-feet telescope. 



1. An enormous ring seen obliquely with a dark centre and a small star 

 at each extremity. 



2. The ring in the constellation Lyra. 



3. The dumb-bell nebula in Vulpicula. 



4. The spiral nebula or brother system in the 20-feet telescope. 



5. A spindle-shaped nebula. 



Plate 9 represents some of the same objects as seen by Lord Rosse. 



1. Nebula in the girdle of Andromeda. 



2. The circular nebula of Lyra. 



3. The dumb-bell nebula in Vulpicula. 



The spiral nebulae of 51 Meissier, as seen by Lord Rosse, 1 in plate 10, 

 represents fig. 4 of plate 8 ; and fig. 2 in the same plate is part of the 

 great nebula in Orion, for the whole has never been seen, on account of 

 extreme remoteness. 



NOTE 237, pp. 32, 427. The motion of the earth is visibly proved by 

 M. Foucault's experiments. If a pendulum be left to oscillate quite freely, 

 the forces producing the oscillations being in the vertical plane, there is no 

 cause that can produce an absolute change in its position with regard to 

 space ; but the motion of the earth changes the position of a spectator with 

 respect to the vertical plane, and he refers his own motion to it, which 

 seems gradually to turn away from its position, precisely as a person in a 

 boat refers his own motion to that of the land, and thus the motion of the 

 earth is truly and visibly proved. 



INDEX. 



