BIOLOGY; 



OR, PHYSIOLOGY, ZOOLOGY, AND BOTANY. 



MOLECULAR FORCES. 



The following- is an extract from the opening address of Prof. 

 Tj^ndall, before the Physical section of the British Association, in 

 1868 : — 



" The tendency on the part of matter to organize itself, to grow 

 into shape, to assume definite forms in obedience to the definite 

 action of force, is all-pervading. It is in the ground on which you 

 tread, in the water you drink, in the air you breathe. Incipient 

 life, in fact, manifests itself throughout the whole of what we call 

 inorganic nature. 



" The forms of minerals resulting from this play of forces are 

 various, and exhibit different degrees of complexity. Men of 

 science avail themselves of all possible means of exploring this 

 molecular architecture. For this purpose they employ in turn, as 

 agents of exploration, light, heat, magnetism, electricity, and 

 sound. Polarized light is especially useful and powerful here. 

 A beam of such lio;ht, when sent in among the molecules of a 

 crystal, is acted on l)y them, and from this action we infer, with 

 more or less of clearness, the manner in which the molecules are 

 arranged. The difference, for example, between the inner struc- 

 ture of a plate of rock-salt and a plate of crystallized sugar is thus 

 strikingly revealed. These differences may be made to disi3lay 

 themselves in phenomena of color of great splendor, the play of 

 molecular force beino; so regulated as to remove certain of the 

 colored constituents of white light, and to leave others with in- 

 creased intensity behind. 



"And now let us pass from what we are accustomed to regard 

 as a dead mineral to a living grain of corn. When it is examined 

 by polarized light, chromatic phenomena similar to those noticed 

 in crystals are observed. And why ? Because the architecture of 

 the grain resembles in some degree the architecture of the crystal. 

 In the corn the molecules are also set in definite positions, from 

 which they act upon the light. But what has built together the 

 molecules of the corn ? I have said regarding crystalline archi- 

 tecture that you ma}', if you please, consider the atoms and mole- 

 cules to be placed in position by a power external to themselves. 

 The same hypothesis is open to j'ou now. But if in the case of 

 crystals you have rejected this notion of an external architect, you 

 are bound to reject it now, and to conclude that the molecules of 

 the corn are self-posited by the forces with which they act upon 



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