586 BIBLIOGRAPHY OF IIERSCIIEL's WRITINGS. 



Herschel, W.: Synopsis of the Wkitings of— Continued. 



A.B. Vol. p. 



1805 95 53 part of the mirror used. Thus the inside rays of a mirror increase 

 the diameter of these disks, whereas the outside rays alone have a 

 greater effect in reducing it than they do when the inside rays are 

 left to join with them. This affords a criterion as to whether a disk 

 is real or spurious. 

 19th Experiment. Trial of Estimations. 

 20th Experiment. Use of the Criterion. 



54 21st Experiment. Measures of the comparative Amount of the spurious Di- 



ameters produced by the Inside and Outside Rays. 

 22d Experiment. Trial of the Criterion on celestial Objects. 



55 22d Experiment. [Another trial.] 



55-61 Observations ox the nature and magnitude of Mr. Harding's 

 lately-discovered star. 



61 Results and application of the experiments and observations. 



62 There is a limit to the size of objects [| second in Herschel's 10-foot 



telescope] above which a mere increase in magnifying power will 



betray the real disk. By the criterion of the outside and inside rays, 



an object of half this angular diameter may be shown to have real 



dimensi^ons, but below this value the telescope cannot distinguish 



^^ between a real and spurious diameter. 



63-64 Remarks on the class of celestial bodies to which the new star be- 



r ... .. I^VBS^?. 9'°*! a justification of the term asteroid as applied to them. 



hOf.-vA ft[^f(tfdJ.Slongh, near Windsor, December 1, 1804. 



1805 95 5^3 Qn the direction and velocity of the Motion of the Sun, and Solar System. 

 7 - - - i^y ^ViLLiAM Herschel, LL. D., F, E. S. Eead May 16, 1805. 



2'3i i)n Maskelyne's Table of the proper motions of 36 stars proves the 



motions of the stars cf the first brightness, such as are probably in 



^^ .,, ., our immediate neighborhood. The chaifges in position of minute 



, ' . , stars that I have ascertained prove that motions are equally carried 



on ih the remotest parts of space. 



233 In 1783 I deduced from the proper motions of stars, with a high de- 



gree of probability, a motion of the sun and solar system towards 

 A Herculis. 



234 The present paper will treat [only] of the direction of the solar 



motion. 



234 Reasons for admitting a solar motion. 



It may appear singular that I should again think it necessary to give 

 reasons for this. The cause is that [in 1783 I proposed to] take 

 away the various proper motions of stars by investing the sun with 

 a contrary one. Now, however, [I find that] the solar motion will 

 reveal so many concealed real motions that we shall have more of 

 them than would be necessary were the sun at rest. Hence the ne- 

 cessity for admitting the solar motion ought to be well established. 



235 Theoretical considerations. 



235 A view of the motions of moons aroimd planets, and these again 



round the sun, may suggest the motion of the latter round some 

 unknown centre. The solar motion was suggested by Lambert; 

 Dr. Wilson has shown its possibility from theoretical principles, 

 and De la Lande its probability. The rotation of the sun indi- 

 cates a motion of translation; the cause of both is unknown. 



236 The periodical stars should be examined with this idea. Conversely 



stars that have a motion in space may be surmised to have also a 

 rotation on their axes. 



1 



