18 Mr. J. Croll on What determines Molecular Motion f— 



idea of a tree of a special kind. The molecules formings say^ an 

 oak tree, must move in relation to one another in a different way 

 from those forming a beech tree or a pine. But however diver- 

 sified may be the motions of the molecules in the different spe- 

 cies of treeSj yet, notwithstanding, all must move in relation to 

 the general idea of a tree. And what holds true of trees holds 

 equally true of every form of plant-life on the globe. And what 

 holds true of the vegetable kingdom holds equally true of the 

 animal kingdom. Each plant and each animal has not only its 

 own particular form, but it has the form of the species to which 

 it belongs — and not only this, but the form of the genus to which 

 the species belongs — and not only the form of the genus, but the 

 form of the family, order, class, and kingdom to which the genus 

 belongs. 



Taking, therefore, the entire molecular movements going on 

 in the organic world, animal and vegetable, we may classify the 

 determination of these movements into kingdoms, classes, orders, 

 families, genera, and species, in the same way as we classify the 

 plants and animals which are the result of these determinations 

 of molecular motion. This is obvious, because this order and 

 unity which the botanist and the comparative anatomist find per- 

 vading nature, owes its existence to the order and unity which 

 exists amongst the determinations of molecular movements. A 

 plant or an animal of a particular species and a particular class 

 exists simply because the molecules of which it is formed had 

 their motions determined according to the objective idea of a 

 plant or of an animal (as the case may be) of the particulal ; 

 species and class. This is not asserting any thing hypothetical ; 

 it is simply stating what actually takes place ; for to say that the 

 molecules of which a tree, for example, is composed must have 

 had their motions determined according to the objective idea of a 

 tree, is just the same thing as saying that the molecules of which 

 a tree is composed must have had their motions determined in 

 relation to an object of the figure of a tree. In nature we have 

 a unity of plan pervading the endless diversity that everywhere 

 prevails, simply because the endless and the almost infinite di- 

 versity of molecular movements take place according to a unity 

 of plan. 



In nature we have a group of molecular movements corre- 

 sponding to the objective idea of each particular object that is 

 being formed. In objects of the same species the groups of mo- 

 lecular movements have a specific resemblance to one another, 

 while in the formation of all objects of the same genus there is 

 a generic resemblance between the groups of molecular move- 

 ments. In the formation of objects of the same family we have 

 a still higher unity, comprehending a still greater number of 



