3 i2 THE POPULAR SCIENCE MONTHLY. 



seconds for the impulse to reach its destination. Thus it will be seen 

 that each dial is slow a certain number of seconds, depending upon its 

 distance from the central station ; nor has it been found that the error 

 of any particular dial is constant. But the error will never be allowed 

 to exceed ten seconds. Should the extension of the system require it, 

 Paris will be divided into six districts (surveyed so that no point in the 

 city shall be over twenty thousand metres from a central station), 

 each provided with its central station equipped in other respects as the 

 one described, but all receiving their compressed air from a common 

 reservoir centrally located. 



However, there are plenty of people in Paris, as there are, doubtless, 

 in every city, for whom a time even ten seconds in error is accurate 

 enough. The system was put into operation there about March 15, 

 1880, and in the first four months there were fifteen hundred subscrib- 

 ers, distributed in six hundred houses. The popularity of the pneu- 

 matic clocks is due to their convenience and cheapness. The rental is 

 only five centimes (one cent) per day for the first clock ; four centimes 

 (eight mills) per day for the second clock ; three centimes (six mills) 

 per day for the third and every subsequent clock rented by the same 

 person ; and the expense of pipes and apparatus is borne by the com- 

 pany. 



JURASSIC BIRDS AXD THEIR ALLIES.* 



By Professor 0. C. MAESH. 



ABOUT twenty years ago, two fossil animals of great interest 

 were found in the lithographic slates of Bavaria. One was the 

 skeleton of Arckceopteryx, now in the British Museum, and the other 

 was the Compsognathus preserved in the Royal Museum at Munich. 

 A single feather, to which the name Arckceopteryx was first applied 

 by Von Meyer, had previously been discovered at the same locality. 

 More recently, another skeleton has been brought to light in the same 

 beds, and is now in the Museum of Berlin. These three specimens of 

 Arc/ueopteryx are the only remains of this genus known, while of 

 Compsognathus the original skeleton is, up to the present time, the 

 only representative. 



"When these two animals were first discovered, they were both 

 considered to be reptiles by Wagner, who described Compsognat hus, 

 and this view has been held by various authors down to the present 

 time. The best authorities, however, now agree with Owen that 

 Arckceopteryx is a bird, and that CompsognatJius, as Gegenbaur and 

 Huxley have shown, is a Dinosaurian reptile. 



* Read before Section D, British Association for the Advancement of Science, at 

 York, September 2, 1881. 



