These double images are made to be viewed as a stereoscopic image. This type of imagery predates photography and was very popular from the mid 1800’s to the mid 1900’s, after Charles Wheatstone showed some stereoscopic photographs at the Royal Society of London. The building presented here is the Hoover Building. This building is located west of London and is a prime example of Art Deco architecture. This building, along with other notable historic buildings including the Battersea Power Station and Earls Court, have been under threat of destruction at some point in their short life. These buildings are unique, and grand.
A good starting point is to use the tip of a pen. Place yourself in front of a stereoscopic pair suited for cross-eyed viewing. Place the pen half way in between and look at the pen. Now, the viewing rays or axes of your eyes should meet or cross at the pen’s tip, and as a consequence, the left eye sees the half image mounted on the right side of the pair behind the pen and vice versa. Finally, the only thing left to learn is shifting the focus back from the pen’s tip to the images behind without changing the direction you are looking at (http://stereopov.ichthyostega.de/viewing.html)
* or, a little more basic, you want to focus somewhere close to the middle point between the images and your self