608 BIBLIOGRAPHY OF HERSCHEl's WRITINGS. 



Herschel, W.: Synopsis of the Writings of— Coutinued. 

 A. D. Tol. p. 



by comparing their distribution to a certain properly modified 



equality of scattering. The equality -which I ^iropose does not re- 

 1817 107 305 quire that the stars should be at equal distances from each other, 



nor is it necessary that all those of the same nominal magnitude 



should be equally distant from us. 



305 It consists in allotting a certain equal portion of space to every star, 



in consequence of which we may calculate how many stars any 

 given extent of space may contain. 

 This arrangement is explained by means of a figure. Plate XV, 

 Fig. 1. 



306 III. ComjMrison of tlie order of magnitudes ivith tlie order of distances. 

 Comparison of the order of distances by the foregoing scheme with 



the magnitudes assigned in Bode's catalogue of 14,144 stars. 

 308 The result of this comparison is, that if the order of magnitudes 

 could indicate the distance of the stars, it would denote at first a 

 gradual, and afterwards a very abrupt, condensation of them ; but 

 that, considering the principle on which the stars are classed, their 

 arrangement into magnitudes can only apply to certain relative 

 distances, and show that, taking the stars of each class, one with 

 another, those of the succeeding magnitudes are farther from lis 

 than the stars of the preceding order. 



308 IV. Of a criterion for ascertaining the profundity or local situation of 



celestial ohjects in space. 



309 It will be admitted that those stars, the light of which we can ex- 



perimentally prove to be J, ^, -^ of the light of any certain 



star of the first magnitude must be 2, 3, 4 times as far from 



us as the standard star, provided the condition of the stars should 

 come up to the supposed mean state of diameter and lustre of the 

 standard star. 

 309 V. Of the equalization of star light. 



309 Star gauging gave rise to an investigation of the space-penetrating 



power of telescopes. 



310 Finding that this might be calculated with reference to the extent of 



the same power of which the unassisted eye was capable, there 

 always remained a desideratum of some sure method by which this 

 last might be ascertained. 

 Description of experimental apparatus. 



311 Method of limiting a^^ertures described. 



313 VI. Of the extent of natural vision. 



313-8 Experiments on stars made in August and December, 1803, and 

 February, 1814. 



314 Arcturus has four times the light of a Andromeda, Polaris, y Ursce, 



and S Cassiopece. a Andromeda is four times as bright as f.i Pegasi, 

 etc., etc. 

 316 Table of projiortional light of stars of various orders. 



318 The distances of clusters cannot be ascertained by the method of 



equalizing star light. 

 VII. Of the extent of telescopic vision. 



319 Experiments which go to show that the diameter of the pupil of the 



human eye is not more than 0.21 inch, and is greater than 0.17 inch 

 when observing with a telescope. It may be assumed 0.2 inch. 



320 VIII. Application of the extent of natural and telescopic vision to the 



probable arrangement of the celestial bodies in space. 



