president's ADDBE88. 21 



Although astronomy gives ample opportunities for the 

 exercise of the imagination when we are dealing with hypotheses 

 concerning the probable composition and movements of the 

 heavenly bodies hundreds of billions of miles away, yet in many 

 of its branches it is very far from being purely a speculative 

 science ; at any rate the assertion of some that it is so is totally 

 misleading, so far as regards the great fundamental laws of 

 gravitation which govern the motions of all celestial bodies. 

 But in comparison with the more practical sciences dealing with 

 terrestrial elements, such as chemistry, geology, and mineralogy, 

 astronomy must always appear somewhat dependent on the 

 imagination of the observer, for the objects of his scrutiny are 

 usually far too distant to ascertain their true characteristics 

 without having some recourse to speculative analogy. How 

 different all this is in chemistry and other experimental sciences. 

 Here the experimenter has no occasion to go beyond what he 

 has before him, as he has the advantage of always being certain 

 of the discoveries that he makes. All that he has to do, if he 

 is in doubt, is to repeat his experiment, and thus he can make 

 sure of the effect of his discovery. Many of you probably will 

 partly agree with the remarks made recently by the Marquis of 

 Salisbury, when addressing the Chemical Society at their 

 late Jubilee meeting, "that of course when a man discovers 

 what happened fifty millions of years ago, it is not so easy to be 

 exactly accurate as to the nature of his discovery ; and when a 

 man discovers what is going on fifty billions of miles away, 

 although the discovery may be probable, it certainly has not the 

 character of certainty that attaches to the discovery of a man 

 who can go back to his laboratory and repeat his experiments. 

 For it must be acknowledged that astronomy is largely composed 

 of the science of things as they probably are, and that geology 

 consists mainly of the science of things that probably were a long 

 time ago, and chemistry is the science of things as they actually 

 are at the present time." Whatever truth there may be in this 

 comparison, his lordship, who is himself a distinguished practical 

 chemist, forgets that in the present advanced teachings of chemis- 

 try, the chemical imagination is essentially mathematical, for the 

 formulse deduced from analysis ordinarily give very little ex- 

 planation of the reason why the combination of elements has 



