SCIENCE LETTER FROM PARIS. 607 



CORRESPONDENCE. 



SCIENCE LETTER FROM PARIS. 



Paris, Dec. 17, i88r. 



Public attention is daily becoming more intensely fixed on the subject of 

 railway brakes and signals. Since a long time specialists have been studying 

 systems of continuous brakes, that is to say, a plan of operating simultaneously 

 on several carriages. It is not a little singular, that from the first, electricity was 

 designed as the agent; as M. Achard, in 1858, proposed an electric brake for the 

 Great Eastern of France. In i860 Messrs. Tremblay & Martin took out a patent 

 for the employment of compressed air as a motive power to regulate the rapidity 

 of locomotives and railway carriages. The trials were not successful. From 

 1861 to 1872 efforts were made to group uncontinuous brakes as patented by 

 Newall, Clarke, Heberlein, etc. In 1872 the Westinghouse brake was introduced 

 into Europe from the United States ; next succeeded the Smith plan of rarified 

 air. Between these two systems, and neither of which is perfect, engineers had 

 to decide. The Smith patent, which was the Tremblay & Martin idea, possessed 

 the advantages of being simple, had no delicate or complicated mechanism, was 

 easily constructed and repaired. But it had the drawback, that the force exercis- 

 ed by the brake could not exceed the pressure of one atmosphere. In the West- 

 inghouse plan, a greater pressure could be employed, since the agent being com- 

 pressed air, several atmospheres could be utilized ; it also presented the advantage 

 of pulling up more promptly masses of matter animated with a grand momentum. 

 But the fear existed, that the valve which gave passage to the compressed air, 

 was too delicate and very difficult to repair ; hence, authorities are nearly divided 

 into two camps, with the balance of the opinion in favor of the Westinghouse 

 brake. However, experience showed the latter could spontaneously get out of 

 order, and suddenly cause a train to come to a full stop ; then to resume travel- 

 hng, it was necessary to undo the brake from carriage to carriage. Further, it 

 was not a fnoderateur check, obedient to the engineer, when descending a decline, 

 etc. Since September last, M. Henry, of the Paris-Lyon Railway, has remedied 

 these defects. A question that the engineering world has yet to agree upon is : 

 Ought brakes to be automatic? The system has the advantage of telling itself, 

 by stopping ; but the stoppages arrive so frequently as to counter-balance superi- 

 ority over the other systems. In France, the leaning is at present decidedly in 

 favor of the Westinghouse, which represents an important progress since twenty 

 years ; but where may it be in another score of years? 



