308 MODEL DIVING-BELL. 



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 for- 

 ward. It is also the principle by which sky-rockets ascend. 

 Now, if naturalists are to be believed, this is exactly the device 

 which Nature has made use of for the motion of sonic species 

 of aquatic insects." 



The living body, the action of whose motive apparatus we 

 are now observing, is the larva of a dragon-fly, and its curious 

 pump performs for its possessor two other important services 

 besides that of propulsion ; the one is to furnish it witli a 

 supply of air, the other to bring within its grasp, by means of 

 the rcverberatory current, a number of the lesser water-insects 

 which constitute its prey. 



Time will only serve now for notice of one more object in 

 this, the aquatic division of our exhibition, but that is an 

 object worthy, like the diving-bell of the " Polytechnic/"' its 

 artificial prototype, of particular attention. Yes, amongst these 

 miniature models is one, as we shall show you, of a diving- 

 bell; though you will hear no tinkling notice of its working 

 and descent, inasmuch as it is usually stationary, or only 

 moveable at pleasure of its diving occupant, of whose inten- 

 tions it would be a difficult matter to give notice. 



Well, here, beside the edge of our canal, moored to an 

 aquatic plant by some silken cables, we perceive, submerged 

 all but the top, a bell or dome not very dissimilar in size and 

 shape to the half of a pigeon's egg. Like that, and like a 



