THE FLYING FROG. 441 



flat and elastic membranes. When simply crawling on the 

 branches, after the manner of tree-lizards, the ribs lie flat 

 against the sides, and the membranes collapse, so that the 

 shape of the body is little different from that of any crawling 

 lizard. 



But the ribs are movable at will, and, when the creature 

 wishes to pass from one tree to another, it extends the ribs, 

 stretches the membranes, and launches itself into the air, 

 exactly as has been narrated of the Flying Squirrel. 



THE lowest figure represents a most extraordinary animal, 

 called the Flying Frog. Only one specimen is believed to be 

 known, and that was discovered in Borneo by Mr. Wallace. 



Here we have an analogy with the bats of the present day 

 and the pterodactyles of the past, namely, the elongation of 

 the toes, and the stretching of a web between them. In the two 

 latter animals, however, only the toes of the two fore-legs are 

 elongated, whereas, with the Flying Frog, the elongation is 

 found in both pairs of limbs. The ends of the toes are fur- 

 nished with adhesive pads, like those of the tree-frogs, to 

 which it is probably related. 



By means of the four membranes, the creature is able to 

 sweep through the air for some distance, and, indeed, this power 

 was the reason why it was caught. It was seen to skim from 

 one tree to another, and was immediately secured. Had it 

 remained sticking on the tree, it would probably have escaped 

 observation. 



WEIGHT OF AIR. 



WE have already noticed that hydrogen gas is fourteen 

 times lighter than air, and infer necessarily that the weight of 

 the atmosphere must be very considerable if so heavy an object 

 as a balloon, with its car, instruments, sand-bags, and pas- 

 sengers, can rise and float in it. 



We are not conscious of its weight, because it permeates us, 

 and the pressure is neutralised. But, in fact, we live at the 

 bottom of a vast ocean which we call the atmosphere ; and as, 

 on an average, there is a pressure of fifteen pounds on every 

 square inch of surface, we have to sustain an almost incredible 



