INSECTS. 221 



constitution. Here then is the diversity of tlie case. The 

 caterpillar cannot meet her companion hi the air. The 

 winged rover disdains the ground. They might never there- 

 fore be brought together, did not this radiant torch direct 

 <,he volatile mate to his sedentary female. 



In this example we also see the resources of art antici- 

 pated. One grand operation of chemistry is the making 

 of phosphorus ; and it was thought an ingenious device to 

 make phosphoric matches supply the place of lighted tapers. 

 Now this very thing is done in the body of the glowworm. 

 The phosphorus is not only made, but kmdled, and caused 

 to emit a steady and genial beam, for the purpose Avhich is 

 here stated, and which I believe to be the true one. 



VI. Nor is the last the only instance that entomology 

 affords, in which our discoveries, or rather our projects, turn 

 out to be imitations of nature. Some years ago a plan was 

 suggested of producing propulsion by reaction in this way : 

 by the force of a steam-engine, a stream of v/ater was to be 

 shot out of the stern of a boat, the impulse of which stream 

 upon the water in the river was to push the boat itself foj-- 

 ward ; it is in truth the principle by which skyrockets 

 ascend in the air. Of the use or practicability of the plan 

 I am not speaking ; nor is it my concern to praise its inge- 

 nuity ; but it is certainly a contrivance. Now, if natural- 

 ists are to be believed, it is exactly the device which nature 

 has made use of for the motion of some species of aquatic 

 insects. The larva of the dragonfly, according to Adams, 

 swims by ejecting water from its tail — ^is driven forward by 

 the reaction of water in the pool upon the current issuing 

 in a direction backward from its body. 



VII. Again, Europe has lately been surprised by the 

 elevation of bodies in the air by means of a balloon. The 

 discovery consisted in finding out a manageable substance, 

 which was, bulk for bulk, lighter than air ; and the appli- 

 cation of the discovery was to make a body composed of this 

 substance bear up, along with its own weight, some heavier 



