ADDRESS. XCl 



duction ; and llic investigation of the consequences of this law, and the 

 explanation thereby of the lunar and planetary disturbances, have afforded 

 a iield for the exercise of the highest mathematical powers on the part of 

 Newton and bis successors. Gradually the apparent anomalies, as they 

 might have been deemed, in the motions of the heavenly bodies were shown 

 to be necessary consequences of the one fundamental law ; and at last, as the 

 result of calculations of enormous labour, tables were constructed enabling 

 the places of those bodies at any given time to be determined years before- 

 hand with astonishing precision. A still more striking step was taken. 

 AYhen it had been shown by careful calculation that the apparent motion of 

 the remotest of the planets then known to belong to our system could not 

 be wholly explained on the theory of gravitation, by taking account of the 

 disturbing powers of the other known planets, Adams in our own country, 

 and Le Verrier in France, boldly reversed the problem, and instead of 

 determining the disturbing effect of a known planet, set themselves to inquire 

 what miist be the mass and orbit of an unknown planet which shall be capa- 

 ble of producing by its disturbing force the unexplained deviations in the 

 position of Uranus from its calculated place. The result of this inquiry is 

 too well known to reqiiire notice. 



After these brilliant achievements, some may perhaps have been tempted 

 to imagine that the field of astronomical research must have been well-nigh 

 exhausted. Small perturbations, hitherto overlooked, might be determined, 

 and astronomical tables thereby rendered still more exact. New asteroids 

 might be discovered by the telescope. More accurate values of the con- 

 stants with which we have to deal might be obtained. But no essential 

 novelty of principle was to be looked for in the department of astronomy ; 

 for such we must go to younger and less mature branches of science. 



Eesearches which have been carried on within the last few years, even 

 the pi'ogress which has been made within the last twelve months, shows 

 how short-sighted such an anticipation would have been ; what an unex- 

 pected flood of light may sometimes be thrown over one science by its union 

 with another ; how conducive accordingly to the advancement of science 

 may be an Association like the present, in which not only are the workers 

 at special sciences brought together in the Sectional Meetings, but in the 

 General Meetings of the Association, and in the social intercourse, which, 

 though of an informal character, is no unimportant part of our procedings ; 

 the cultivators of different branches of science are brought together, and 

 have an opportunity of enlarging their minds by contact with the minds of 

 others, who have been used to trains of thought of a very different character 

 from their own. 



The science of astronomy is indebted to that of optics for the principles 

 whch regulate the construction of those optical instruments which are so 

 essential to the astronomer. It repaid its debt by furnishing to optics a 

 result which it is important we should keep in view in considering the 

 nature of light. It is to astronomy that we are indebted for the first proof 

 we obtained of the finite velocity of light, and for the first numerical deter- 

 mination of that enormous velocity. Astronomy, again, led, forty-four years 

 later, to a second determination of that velocity in the remarkable pheno- 

 menon of aberration discovered by Bradley, a phenomenon presenting spe- 

 cial points of interest in relation to the nature of light, and which has given 

 rise to some discussion, extending even to the present day, so that the Astro- 

 nomer Eoyal has not deemed it unworthy of investigation, laborious as he 

 foresees the trial is likely to prove, to determine the constant of aberration 

 by means of a telescope having its tube fiUed with water. 



