THE STELLAR UNIVERSE. 



through its consequences, to state the arguments by which it is 

 supported and opposed ; and it is the less necessary to do so, seeing 

 that such an hypothesis is not needed to explain appearances which 

 are so much more obviously and simply explicable by the admission 

 of a gradation of distances. 



80. The apparent forms of these objects are extremely various, 

 and subject to most extraordinary and unexpected changes, 

 according to the magnifying power under which they are viewed. 

 This ought, however, to excite no surprise. The telescope is an 

 expedient by which a well-defined and strongly illuminated 

 optical image of a distant object is formed so close to the observer, 

 that he is enabled to view it with microscopes of greater or less 

 power, according to the perfection of its definition, and the inten- 

 sity of its illumination. Now, it is known to all who are familiar 

 with the use of the microscope, that the apparent form and 

 structure of an object change in the most remarkable and unex- 

 pected way when viewed with different microscopic powers. The 

 blood, for example, which viewed with the naked eye, or with low 

 powers, is a uniformly red fluid, appears as a pellucid liquid, 

 having small red discs floating in it, when seen with higher 

 powers. Like effects are manifested in the cases of the nebulas, 

 when submitted to examination with different and increasing 

 magnifying powers, of which we shall presently show many 

 striking examples. 



Stellar clusters are generally roundish or irregular patches. The 

 stars which compose them are always much more densely crowded 

 together, in going from the edges of the cluster towards the centre, 

 so that at the centre they exhibit a perfect blaze of light. 



The apparent form is that of a section of the real form, made 

 by a plane at right angles to the visual ray. If the mass had a 

 motion of rotation, or any other motion by which it would change 

 this plane, so as to exhibit to the eye successively different sections 

 of it, its real form could be inferred as those of the planets have 

 been. But there are no discoverable indications of any such 

 motion in these objects. Their real forms, therefore, can only be 

 conjectured from comparing their apparent forms with their 

 structural appearance. 



The clusters having round apparent forms, and of which the 

 stars are rapidly more dense towards the centres, are inferred to 

 be either globular or spheroidal masses of stars, the greater 

 apparent density in passing from the edges to the centre being 

 explained by the greater thickness of the mass, in the direction 

 of the visual line. Clusters of irregular outline which show also 

 a density increasing inwards, are also inferred, for like reasons, to 

 be masses of stars, whose dimensions in the direction of the visual 

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