1869.] ( 579 ) 



THE BRITISH ASSOCIATION FOR THE ADVANCEMENT 

 OF SCIENCE. 



MEETING AT EXETEK, August, 1869. 

 Tece Pkesident's Address. 



The past twelve months have been characterized by steady work 

 rather than for many brilhant scientific results. Investigators have 

 been rather collecting particulars than forming generahzations. 

 The dominant scientific result of the year has been the extended 

 knowledge which we have gained of the constitution of the sun and 

 heavenly bodies, and this met with full recognition in the inaugural 

 address of the President, G. Gr, Stokes, M.A., Sec. E.S., which was 

 delivered in the Victoria Hall, Exeter, on the 18th of August. 



After briefly alluding to the objects of the Association, the Pre- 

 sident gave some account of the most recent progress of science, 

 selecting especially from those branches with which he was more 

 familiar, some examples which might prove to be of pretty general 

 interest. Amongst the various branches of physical science. Astro- 

 nomy occupies in many respects a foremost rank. The science of 

 astronomy is indebted to that of optics for the principles which regu- 

 late the construction of those optical instruments which are so essen- 

 tial 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 determination of that enormous velocity. Astronomy, 

 again, led, forty-four years later, to a second determination of that 

 velocity in the remarkable phenomenon of aberration discovered by 

 Bradley, a phenomenon presenting special points of interest in 

 relation to the nature of Hght. If, in respect of these phenomena, 

 optics received much aid from astronomy, the latter science has 

 been indebted to the former for information which could not other- 

 wise have been obtained. The motions and the masses of the 

 heavenly bodies are revealed to us, more or less fully, by astrono- 

 mical observations ; but w^e could not thus become acquainted with 

 the chemical nature of these distant objects. Yet, by the application 

 of the spectroscope to the scrutiny of the heavenly bodies, evidence 

 has been* obtained of the existence therein of various elements 

 known to us by the chemical examination of the materials of which 

 our own earth is composed ; and not only so, but light is thrown 

 on the state in which matter is there existing, which, in the case of 

 nebulae especially, led to the formation of new ideas respecting 



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