FLIGHT OF INSECTS. 359 



sessed by the Lucanns, or stag-beetle, had been 

 given to the elephant, that animal would have 

 been capable of tearing up by the roots the 

 largest trees, and of hurling huge rocks against 

 his assailants, like the giants of ancient mytho- 

 logy. 



But while we must admit that all these facts 

 indicate a remarkable degree of energy in the 

 contractile power of the muscular fibres of in- 

 sects, we should at the same time recollect that 

 the diminutive size of the beings which display 

 those powers is itself the source of a mechani- 

 cal advantage not possessed by larger animals. 

 The efficacy of all mechanical arrangements 

 must ultimately depend on a due proportion be- 

 tween the moving and the resisting forces : hence 

 mechanism of every kind must be adjusted with 

 reference not merely to the relative, but to the 

 absolute dimensions of the structures themselves. 

 This will be evident when we consider that the 

 forces which are called into action are resisted 

 by the cohesion of the particles composing the 

 solid parts of the machine : and this cohesion, 

 being not a variable, but a constant and definite 

 force, must necessarily limit the dimensions of 

 every mechanical structure, whether intended 

 for stability or for action. An edifice raised 

 beyond a certain magnitude, will not support 

 itself, because the weight of the materials in- 

 creases more rapidly than the strength. How 



