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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 subscribers, distributed in six hundred houses. The popularity of the pneumatic 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 company.

 

JURASSIC BIRDS AND THEIR ALLIES.[1]
By Professor O. C. MARSH.

ABOUT twenty years ago, two fossil animals of great interest were found in the lithographic slates of Bavaria. One was the skeleton of Archæopteryx, 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 Archæopteryx 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 Archæopteryx 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 Compsognathus, and this view has been held by various authors down to the present time. The best authorities, however, now agree with Owen that Archæopteryx is a bird, and that Compsognathus, as Gegenbaur and Huxley have shown, is a Dinosaurian reptile.

  1. Read before Section D, British Association for the Advancement of Science, at York, September 2, 1881.