THE STELLAR UNIVERSE. 



the star preserves all its lustre until the moment it comes into 

 contact with the dark edge of the moon's disc, and then it is 

 instantly extinguished, without the slightest appearance of 

 diminution of its brightness. 



29. It may be asked then, if such be the case, and if none of the 

 stars, great or small, have any discoverable magnitude at all, with 

 what meaning can we speak of stars of the first, second, or other 

 orders of magnitude ? The term magnitude thus applied, was 

 used before the invention of the telescope, when the stars, having 

 been observed only with the naked eye, were really supposed to 

 have different magnitudes. We must accept the term now to 

 express, not the comparative magnitude, but the comparative 

 brightness of the stars. Thus, a star of the first magnitude 

 means of the greatest apparent brightness ; a star of the second 

 magnitude, means that which has the next degree of splendour, 

 and so on. But what are we to infer from this singular fact, 

 that no magnifying power, however great, will exhibit to us a 

 %star with any sensible magnitude ? must we admit that the 

 optical instrument loses its magnifying power when applied to the 

 .stars, while it retains it with every other visible object ? Such 

 a consequence would be eminently absurd. "We are therefore 

 driven to an inference regarding the magnitude of stars, as 



astonishing and almost as inconceivable as that which was 

 forced upon us respecting their distances. We saw that the 

 entire magnitude of the annual orbit of the earth, stupendous as 

 it is, was nothing compared to the distance of one of those bodies, 

 and, consequently, if that orbit were filled by a sun, whose mag- 

 nitude would therefore be infinitely greater than that of ours, 

 such a sun would not appear to an observer at the nearest star of 

 .greater magnitude than 1" ; consequently, would have no magni- 

 tude sensible to the eye, and would appear as a mere lucid point 

 to an observer at the star ! "We are then prepared for the infer- 

 ence respecting the fixed stars which telescopic observations lead 

 to. The telescope of Sir William Herschel, to which he applied a 

 power of 6000, did undoubtedly magnify the stars 6000 times, 

 but even then their apparent magnitude was inappreciable. 

 We are then to infer that the distance of these wonderful bodies 

 is so enormous, compared with their actual magnitude, that their 

 apparent diameter, seen from our system, is above 6000 times less 

 than any which the eye is capable of perceiving. 



30. It appears, therefore, that stars are rendered sensible to 

 the eye, not by subtending a sensible angle, but by the light they 

 emit. It has been already explained,* that an illuminated or 



* See Tract on "The Eye." 

 183 



