44 THE PROGRESS AND SPIRIT OF 



the vast resources of analysis having tended to multiply ele- 

 ments upon us, rather than to abridge their number. Some 

 approach in this direction has, however, been made through 

 the law of isomorphism; which, in showing relations of 

 mutual substitution between certain elementary bodies hav- 

 ing other curious resemblance of physical properties, has led 

 to their arrangement in groups ; preparatory, it may be 

 hoped, to some future discovery which will give a common 

 basis to all the bodies thus related. The most remarkable of 

 these groups is that comprising chlorine, iodine, and bromine. 

 Arsenic and phosphorus selenium and sulphur and the 

 group of the platinum metals, are other examples of these 

 singular relations, to which, in connection with the law of 

 definite proportions, the labours of the chemist are sedulously 

 directed ; not solely for instant results, but with the prospect 

 constantly before him of those higher truths, to which some 

 one single discovery may perchance open the way. The 

 present methods of chemical enquiry are peculiarly fitted to 

 this critical examination of the simple bodies ; while in the 

 spectrum analysis that extraordinary discovery of which 

 we have spoken we find the promise of results scarcely 

 yet compassed even by the imagination. Electricity, again, 

 equally powerful and delicate as an instrument of research, 

 has been, and must ever be, an especial aid in the prosecu- 

 tion of an object worthy of all the labour that can be given 

 to its attainment. 



We have already spoken at some length, of Light as an 

 element in the universe ; and of its properties as it comes 

 transmitted to us from the Sun and other worlds in space. 

 But much more might be said, had we space for it, of those 

 wonderful phenomena whether derived from solar or arti- 

 ficial light which have exercised the highest genius of 

 modern science, and largely invoked mathematics as an aid 

 to experimental enquiry. If we have not yet reached a true 



