Steel Stretches! When an engineer makes that statement, his listeners are skeptical. But it does, according to the Bridge engineers. They will tell you that due to the constantly varying winds and temperature at the Bridge site, the Bridge is always moving. Take the cables for example. Engineers say if they were detached and laid out on the ground they would be 21 feet shorter than their hanging length. That measurement is the “stretch” caused by the immense load they support. These factors were an important element in the designing of the Bridge, and the elements enter into them… — Official souvenir program, Golden Gate Bridge fiesta : celebrating the opening of the world’s longest single span, San Francisco, California, May 27 to June 2, 1937
The Outdoor Exploratorium in San Francisco has a telescope 2 miles away where you can see the Golden Gate Bridge rise and fall a total of 16 feet depending on the weather.
This video will demonstrate the Bridge Thermometer in action.