The stereoscope was a popular entertainment and educational object in use in the late 19th century. Stereovision or 3-D is the natural way that we see nature, since we see two images, one with each eye that are processed into one image in the brain. When we look at pictures we coordinate the image with what we see in real life. Cameras can be arranged to simulate this effect. 3-D effects can be used in aerial photography, x-rays, microscopes, astronomy, eye therapy, and testing driver's vision. Television production companies are working on the development of 3-D television.