Pleasant Ways in Science. - 465 



opaque, and somewhat less fusible.* It has a specific gravity of 

 1"515, while phosphorus becomes reconverted into the vitreous 

 variety by a temperature not exceeding 122°. A third form is 

 obtained by suddenly casting melted phosphorus ; it is per- 

 fectly black and opaque ; while a fourth, or viscous modification, 

 analogous to viscous sulphur, may be obtained by heating very 

 pure phosphorus to near its boiling point, and suddenly cooling 

 it. A fifth form occurs in the shape of red scales, which are 

 obtained by the spontaneous sublimation of phosphorus in the 

 Torricellian vacuumf when exposed to the rays of the sun." 



This red phosphorus may be obtained by other means, and 

 has been extensively used in the manufacture of lucifer matches, 

 a most unhealthy business when common phosphorus is em- 

 ployed. It is not soluble in some liquids, like bisulphide of 

 carbon, which dissolves common phosphorus. Instead of 

 catching fire in the open air, as common phosphorus does at a 

 comparatively low temperature, it must be heated to 300° be- 

 fore such action takes place, and instead of acting like common 

 phosphorus as a powerful irritant poison, it may be swallowed 

 with impunity. 



It is impossible to place limits to the variety of substances 

 that may be produced by different modes of arranging the 

 same quantities of the same elements in various patterns. We 

 recognize boundless diversity, but when does the identity stop ? 

 Is there only one ultimate substance capable of existing in 

 different states ? It is obvious that speculations concerning 

 identity and change have a wide field in the regions over which 

 chemistry presides. We have merely indicated some of the 

 simplest, and with these for the present must be content. 



The astonishing changes which animals undergo from the 

 egg to their complete form illustrate other phases of the same 

 theme. All creatures that we know of originate in a bud or 

 an egg. Probably the egg always appears at some part of the 

 series, and it is now certain that the most developed creatures, 

 the mammalia, thus commence their being. Thus man and the 

 silkworm both spring from eggs. In the higher forms of 

 animals the hatching process precedes birth, in the lower the 

 egg is born into the world, and changes take place within it 

 which eventuate in the appearance of the infant stage of the 

 creature that is hatched. 



Natural history abounds in remarkable illustrations of the 



* M. Baudrimont affirms that white phosphorus is not an allotropic form 

 of common phosphorus, and that it only varies from the latter by having its 

 surface corroded through partial combustion. If this be so, the general argument 

 is not affected. M. Baudrimont' s paper is in Comptes Mendus, 13th Nov., 1865. 



f The upper and empty part of a barometer tube is a Torricellian vacuum. 

 The air can only press up into the tube a column of mercury equal to its own 

 weight. The tube is filled in the first instance, and the mercury falls till the air 

 column is balanced. 



VOL. VIII. — NO. VI. H II 



