NEBULuE. 



which the brightness increases rapidly towards the centre, which 

 it very generally does, it may be probably conjectured that their 

 forms are globular or spheroidal, for the reasons already explained 



Fig. 20. 



in relation to the clusters, and this becomes the more probable 

 when it is considered, that these nebulae are in fact clusters, the 

 stars of which are reduced to a nebulous patch by distance. 



25 



