NATURAL PHILOSOPHY. 153 



they are heated. Tims, Arnott, in his Physics, designates it as "a 

 most extraordinary exception to the law of expansion by heat and 

 contraction by cold," producing unspeakable benefits in nature, etc. 



In Brande's Dictionary of Science it is said, " In general, all liquids 

 expand and contract in proportion as they are heated and cooled, but 

 to this law there is a remarkable and anomalous exception in regard 

 to water." 



In Kemp's Phases of Matter, London, 1855, we are told, "There 

 is a most remarkable exception to this law of expansion in the case of 

 water. Ice, as every one knows, swims upon water, and of course is 

 lighter, that is to say, heat does not expand ice, but, on the contrary, 

 contracts it. Whatever may be the cause, it is one of the most strik- 

 ing instances of design that can be witnessed in nature, and were it 

 not for it, the globe would be scarcely habitable by man. Did water 

 obey the usual law in this respect, it would fall to the bottom as fast 

 as formed." 



Considering the progress of science down to the close of the eigh- 

 teenth century and its still further advances to the present day, it is sin- 

 gular that this alleged anomaly should have been so long taken for 

 granted and stereotyped in works on natural philosophy. It is many 

 years since it was questioned by members of the Philadelphia Mechan- 

 ics' Institute, because of its inconsistency with facts familiar to them. 

 It was stated that it presented no " remarkable," " peculiar," " curious," 

 " extraordinary," or " anomalous" exception, nor any exception at all 

 to any law, but was in strict accordance with the one that governs 

 the solidification of liquids that if ice did not float, the fact would be 

 an anomaly. 



It was affirmed that, if our lakes and rivers were fluid metals, with 

 their surfaces congealed in winter, the solid portions would swim as ice 

 swims ; and the proofs offered were that pigs of lead and tin float in 

 liquid lead and tin, and that the like takes place with gold and silver, 

 zinc, copper, and iron, as may be daily witnessed in the factories. 

 The inference seemed to be that most, if not all, solids are less dense 

 than are their liquids at certain temperatures, and those who doubted 

 this were asked to name a liquid, either vegetable, animal, mineral, 

 or metallic, in which portions solidified do not swim. \\ ax, pitch, rosin, 

 fat, sugar, sulphur, and other substances, were named as affording no 

 support of the common doctrine. 



In passing into the solid state, the molecules of every liquid assume 

 an arrangement more or less peculiar to it, and, is this must take ef- 

 fect at some point of the decreasing temperature, it matters not where 

 that point is as respects the common law of expansion. It no more 

 affects that law than the journey of a traveller is affected by his stop- 

 ping a moment to exchange a word with a friend. It neither affects 

 his previous nor his subsequent progress has, in fact, nothing to do 

 with either. 



The temperature of solidification of course differs in different sub- 

 stances, and so does the effect. It is the molecular arrangement that 

 diversifies the crystalline structures, and consequently the properties 

 of solids; that gives to each a "grain" and character peculiar to 

 itself. In the soft metals, the crystalline texture would hardly be sus- 

 pected, but it may be vividly brought out, even in lead, by crushing a 



