Keywords: PSM V54 D324 Optical illusion with cubes.png en Optical illusion with cubes 1899 http //www archive org/details/popularsciencemo54newy Popular Science Monthly Volume 54 Jastrow Joseph The Mind's Eye p 299-312 author PD-old PD-US Uploaded with UploadWizard Popular Science Monthly illustrations/Volume 54 Necker cubes |