282 CURREXT TOPICS. [J. F. I.

trips. A retarding device then interrupts the process of switching for a duration of 5 seconds so that the turbine does not start up unnecessarily should full voltage reappear across the bus bars. If voltage fails to reappear, a master relay switches into the circuit, causing the automatic starting process to continue. A series of relays operating in their proper order starts the turbine and when the generator voltage has reached 420 the three house transformers are disconnected and the main breaker of the emergency generatro is closed.

R. H. 0.

The Moscow Subway.-(Transit Journal, Vol. 79, No. 6.) On April 22, the first section of 7.1 miles of the Moscow, Russia subway was completed. It connects two of the most populous suburbs through the heart of the business district. When the entire system is completed it will be about fifty miles long and it is laid out radially, twelve lines running outward from the central part of the city with a belt line joining the ends of the radiating subway lines. The diameter of the tunnels is 18 ft., permitting use of wide and com- fortable cars. No two stations are exactIy alike, which enhances architectural interest and aids passengers in identifying them, They are finished in marble, polished granite, majolica and non- ferrous metals.

In tunneling, the natural difficulties were so great that in 1932, after 6,000 workers had unsuccessfuIly attempted a number of tunnels, several experts advised the abandonment of the project as impossible. Practically all known construction methods were tried out including the British shield system, the French caisson system, the Belgian double passage, artificial freezing and the American “flying arch.” For tunneling through solid ground the latter was demonstrated to be cheaper and quicker than the Belgian method. Late in 1932, a method was discovered of treating the subsoil with chemicals which held the tunnel wall together until the concrete linings could be completed.

The cars are 61% ft. long and built entirely of metal. Automatic devices stop them in the event the track ahead is occupied. It is estimated that the subway will carry about 128 million passengers this year.

R. H. 0.

Standardized Rupture Disks.+ Chem. & Met., 42, 260.) The development of the frangible disk as a protective device for unfired pressure vessels has been given considerable impetus by the work of M. E. BONYUN. Briefly the tests consisted of fastening metal