CONTINUITY. 195 



extent, in experiments with this class of substances. It is not 

 a problem to the solution of which there seems any insuper- 

 able difficulty ; the reason why it has not been solved is, I 

 incline to think, that the great practical opticians have no 

 time at their disposal to devote to long tentative experiments 

 and calculations; and on the other hand the theoretic opticians 

 have not the machinery and the skill in manipulation requisite 

 to give the appropriate degree of excellence to the materials 

 with which they experiment ; yet the result is worth labouring 

 for, as, could the defect be remedied, the refracting telescope 

 would make nearly as great an advance upon its present state 

 as the achromatic did on the single lens refractor. 



While gravitation, physical constitution, and chemical 

 analysis by the spectrum show us that matter has similar 

 characteristics in other worlds than our own, when we pass to 

 the consideration of those other attributes of matter which 

 were at one time supposed to be peculiar kinds of matter 

 itself, or, as they were called, imponderables, but which are 

 now generally, if not universally, recognised as forces or modes 

 of motion, we find the evidence of continuity still stronger. 



When all that was known of magnetism was that a piece 

 of steel rubbed against a particular mineral had the power of 

 attracting iron, and, if freely suspended, of arranging itself 

 nearly in a line with the earth's meridian, it seemed an ex- 

 ceptional phenomenon. When it was observed that amber, if 

 rubbed, had the temporary power of attracting light bodies, 

 this also seemed something peculiar and anomalous. What 

 are now magnetism and electricity as known to us ? Forces so 

 universal, so apparently connected with matter, as to become 

 two of its invariable attributes, and that to speak of matter 

 not being capable of being affected by these forces would 

 seem almost as extravagant as to speak of matter not being 

 affected by gravitation. 



So with light, heat, and chemical affiinity, not merely is 

 every form of matter with which we are acquainted capable 

 of manifesting all these modes of force, but so-called matter 

 supposed incapable of such manifestations would to most 

 minds cease to be matter. 



Further than this it seems to me (though, as I have taken 



o 2 



