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In taking over the interests of the Interlocking Switch 
and Signal Company, it had acquired the patents of H. 
Tilden and F. S. Guerber for Hydraulic Interlocking, the 
first installation of which was made at East St. Louis in 
1882. This system gave Mr. Westinghouse the idea of 
using compressed air for switch and signal operation, the 
result being the Hydro-Pneumatic System wherein control 
was furnished by liquid under pressure, the operating 
power being compressed air. Later developments brought 
forth the Electro-Pneumatic System, which is in use today 
and in which the control is by electricity, the operating 
power compressed air. 
Broadening its activities in 1884, the Company began 
the manufacture of electric lamps and electric lighting 
apparatus under the Stanley and Westinghouse patents. 
This business grew so rapidly that the Westinghouse Elec- 
tric Company (now the Westinghouse Electric and Manu- 
facturing Company) was organized to take it over. In 
1886, the Electric Company bought the Garrison Alley 
property from the Union Switch & Signal Company, and 
the latter, seeking a new location, purchased the plant of 
the old Swissvale Car Works at Swissvale, eight miles east 
of Pittsburgh, whence it moved in 1887 and which site it 
still occupies. 
The business and property of the National Switch and 
Signal Company were purchased in 1898. This purchase 
ncluded the assets of the Johnson Railroad Signal Com- 
pany which had previously been absorbed by the National 
Company. 
In 1901, the Company completed the erection of a new 
plant at Swissvale. A portion of this plant was destroyed 
by fire in 1917, but was promptly rebuilt and today the 
ndustry boasts one of the most modern and best equipped 
‘actories in the Pittsburgh District, with a force of close to 
5.000 employees. 
The purchase of the total outstanding stock, amounting 
lo approximately $6,700,000, by the Westinghouse Air 
Brake Company, was consummated in March, 1917, but 
the Company still remains under separate management 
with the following officers: W. D. Uptegraff, Chairman of 
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