This subject is treated under eight different heads:—1. On the law of visible direction in Monocular vision. 2. On the law of visible direction in Binocular vision. 3. On vision of objects of three dimensions, by monocular vision; by binocular vision. 4. On the binocular vision of figures of different magnitudes. 5. On the cause of the perception of objects in relief by the coalescence of dissimilar pictures. 6. On the doctrine of corresponding points. 7. On the vision of cameos and intaglios. 8. On the change in the apparent position of the drawings of solid bodies.