250 FRAGMENTS OF SCIENCE 



every change of service: starting as a beggar with scarce 

 a rag of 'property' to cover its bones) it turns up as a 

 prince when large undertakings are wanted. 'We must 

 radically change our notions of matter,' says Professor 

 Tyndall; and then, he ventures to believe, it will answer 

 all demands, carrying 'the promise and potency of all terres- 

 trial life.' If the measure of the required 'change in our 

 notions' had been specified, the proposition would have 

 had a real meaning, and been susceptible of a test. It is 

 easy travelling through the stages of such a hypothesis; 

 you deposit at your bank a round sum ere you start, and, 

 drawing on it piecemeal at every pause, complete your 

 grand tour without a debt." 



The last paragraph of this argument is forcibly and 

 ably stated. On it I am willing to try conclusions with 

 Mr. Martineau. I may say, in passing, that I share his 

 contempt for the picturesque interpretation of nature, if 

 accuracy of vision be thereby impaired. But the term 

 Yorstellungs-fahigkeit, as used by me, means the power 

 of definite mental presentation, of attaching to words the 

 corresponding objects of thought, and of seeing these in 

 their proper relations, without the interior haze and soft 

 penumbral borders which the theologian loves. To this 

 mode of "interpreting nature" I shall to the best of my 

 ability now adhere. 



Neither of us, I trust, will be afraid or ashamed to 

 begin at the alphabet of this question. Our first effort 

 must be to understand each other, and this mutual under- 

 standing can only be insured' by beginning low down. 

 Physically speaking, however, we need not go below the 

 sea level. Let us then travel in company to the Caribbean 

 Sea, and halt upon the heated water. What is that sea, 



