OF ARTS AND SCIENCES. 157 



tions were made by Celoria with a telescope of good quality, 10 cm. in 

 aperture, and capable of showing stars of the eleventh magnitude 

 under favorable conditions (C. 3). 



The general result is obviously that stars of medium magnitudes are 

 much more uniformly distributed over the sky than the faint stars 

 which make up the mass of the Milky Way, and somewhat more 

 uniformly than the stars visible to the naked eye. From the Milan 

 observations alone we should infer that the ratio of light from the 

 Milky Way, in its brighter regions, to that from the darker portions 

 of the sky, might be expressed in stellar magnitudes by about 1.2. 

 This assumes that the average magnitude of the stars observed in the 

 brighter and fainter regions was the same, and the assumption is prob- 

 ably justifiable. But with Herschel the case was very different. In 

 the darker regions, his telescope showed no greater abundance of stars 

 than Celoria's, while it disclosed twenty times as many in the brightest 

 regions. It should be noted, however, that the region explored at 

 Milan did not include the immediate neighborhood of the galactic pole. 

 The numbers for Celoria's standard area are as follows (C. 4G) : — 



Celoria : maximum 15.1G, minimum 4.98. 

 Herschel: " 301.16, " 4.81. 



The 286 additional stars distinguishable by Herschel's instrument 

 in the brighter region must apparently be regarded as two or three 

 magnitudes fainter, on the average, than the fifteen stars visible to both 

 observers. If they were of equal magnitude with these fifteen, 

 they would furnish nineteen twentieths of the light emitted by the 

 region (neglecting any stars still fainter), which means that they 

 would increase the brightness of the region by an amount to be 

 denoted by 3.2 magnitudes. As it is, we cannot assume this increase 

 of brightness to exceed one magnitude. Since we found the result 

 1.2 for the difference of magnitude between the regions of maximum 

 and minimum density according to the Milan observations, we shall 

 have a difference of little more than two magnitudes as the result of 

 Herschel's observations according to Celoria's reduction.* 



If the inequality of distribution among stars too faint to be sepa- 

 rately visible to Herschel should resemble or surpass that of the 

 fainter stars which he observed, a higher estimate of the relative 

 brightness of the Milky Way would result. But in the absence of 

 further information, we may perhaps make a sufficient allowance for 



* See also, for confirmation, the Cape Observations of the younger Herschel, 

 pp. 373-383. 



