610 THE PKINCIPLES OF SCIENCE. [chap. 



It is remarkable that water, though the most common 

 of all fluids, is distinguished in almost every respect by 

 extreme qualities. Of all known substances water has the 

 highest specific heat, being thus peculiarly fitted for the 

 purpose of warming and cooling, to which it is often put. 

 It rises by capillary attraction to a height more than twice 

 that of any other liquid. In the state of ice it is nearly 

 twice as dilatable by heat as any other known solid 

 substance.^ In proportion to its density it has a far 

 higher surface tension than any other substance, being 

 surpassed in absolute tension only by mercury ; and it 

 would not be difficult to extend considerably the list of its 

 remarkable and useful properties. 



Under extreme instances we may include cases of re- 

 markably low powers or qualities. Such cases seem to 

 correspond to what Bacon calls Clandestine Instances, which 

 exhibit a given nature in the least intensity, and as it 

 were in a rudimentary state.^ They may often be im- 

 portant, he thinks, as allowing the detection of the cause 

 of the property by difference. I may add that in some 

 cases they may be of use in experiments. Thus hydrogen 

 is the least dense of all known substances, and has the least 

 atomic weight. Liquefied nitrous oxide has the lowest 

 refractive index of all known fluids.^ The compounds of 

 strontium have the lowest dispersive power. It is obvious 

 that a property of very low degree may prove as curious 

 and valuable a phenomenon as a property of very high 

 degree. 



"O* 



The Detection of Continuity. 



We should bear in mind that phenomena which are in 

 reality of a closely similar or even identical nature, may 

 present to the senses very different appearances. Without 

 a careful analysis of the changes which take place, we may 

 often be in danger of widely separating facts and processes, 

 which are actually instances of the same law. Extreme 

 difference of degree or magnitude is a frequent cause of 



' Philosophical Magazine, 4th Series, January 1 870, vol. xxxix. p. 2. 

 2 Novum Orfjanum, bk. ii. Anhoiisin 25. 



•' Faraday's Experivuntal Researches in Chemistry and Physics, 

 P- 93- 



