22 president's address. 



certain properties. Two substances having different properties 

 not uncommonly give, on analysis, formulae almost identical. 

 Hence chemists endeavour to obtain a correct grouping of the 

 elements, as well as of their quantitative proportions, and in 

 this operation the scientific imagination has most arduous work 

 to perform. 



But though imagination must necessarily enter deeply into 

 some astronomical problems, it is a very different thing from the 

 faculty that substitutes conjecture or speculation for ascertained 

 fact. Original scientific research in all its branches could 

 scarcely be carried on without bringing the imaginative powers 

 into action, or we could have none of the fruitful yet purely 

 tentative theories by which the results of research are system- 

 atized. Sometimes a certain number of facts may be joined 

 together to form an intellectual frame- work, from which the 

 scientific imagination may, by analogy, carry it into the 

 neighbouring region of the unknown. These tentative theories 

 may sometimes turn out to be wonderfully exact ; at other times 

 they may have to be abandoned, but in either case they offer 

 most valuable assistance to the inquirer in researches of this 

 nature. This style of reasoning is particularly noticeable in 

 astronomy, especially in some deductions derived from spectrum 

 analysis ; in the problem of the motion and direction of the sun 

 and its system in space ; and in such a speculative subject as the 

 new meteoritic hypothesis. In the consideration of all these 

 delicate researches, imagination of some form must naturally 

 enter very fully into combination with much that is derived from 

 undoubted facts capable of scientific explanation. 



Imagination, however, has very little part in our conceptions 

 of the movements of the sun, moon, and planets in their respec- 

 tive orbits. These have been determined with an accuracy 

 almost marvellous, the proof of which is daily presented to our 

 minds by the never failing recurrence of the various astronomical 

 phenomena at the predicted times given by calculation. So 

 perfect are the existing theories of the movements of the 

 different members of the solar system, that the positions of the 

 sun and moon may be ascertained for any given moment in the 

 past, present, or future, within a fraction of a second of time, 

 while those of the planets may also be determined within very 



