552 SCIENTIFIC RECREATIONS. 



(4) Planetary Nebulae. 



(5) Stellar Nebulae. 



(6) Nebulous Stars. 



We learn also from the foregoing authority that Nebulse affect a certain 

 district ; that is, they have, as it were, a preference for it, and are not dis- 

 tributed in a random manner over the heavens, and are found in Leo, Leo 

 Minor, Ursa Major, Canes Venatici, Coma, Bootes, and Virgo, and more 

 sparingly .in Aries, Taurus, Orion, Perseus, Draco, Hercules, Lyra, etc. 

 Nebulse are found associated with stars, as is the case with 77 Argus ; these 

 are called nebulous stars, and in the case of this particular star many very 

 interesting investigations have been made. The Nebulae are as equally variable 

 as the stars they surround. 



What is termed the Nebular Hypothesis was put forward by La Place, 



and by it he endeavoured to account 

 for the regular development of the 

 stellar system, which is supposed to 

 have originated from an immense 

 nebular ' cloud. This immense mass 

 would rotate and contract, and the 

 outer portions would separate and 

 develop in rings like Saturn's rings. 

 Then the rings break into separate 

 portions, and each portion condenses 

 into a planet, or the small " bits" tra- 



Fig. 626. Nebula; in Perseus. . _ . ... . - - . 



vel round the sun like asteroids, and m 



this manner various systems were formed. This theory was considered to 

 be quite exploded when stars were discerned in nebulae by the more recent 

 telescopes ; but then the spectroscope came to our aid, and it was discovered 

 that there were some nebulae which are simply masses of glowing gas or 

 aggregations of stones which are dashing 

 against each other in so forcible a manner 

 as to produce heat and luminosity. Mr. 

 Lockyer appears to favour the latter theory 

 as to nebulae. 



Mr. Proctor, however, has put forward 

 a hypothesis that the star or meteor showers 

 are the original cause of the sidereal system, 

 and this rain of meteors has fallen for all 

 time, gradually consolidating into orbs. The 

 fact that the constituents of sun, earth and Fig - ^-Nebulae in Canes venatio. 

 planets, corr. ets and meteors being fundamentally the same lends probability 

 to this hypothesis, which is fully explained by the author. 



