Beginning of Essay
Comprehension of anything requires a framework already in place in order to place it in out sphere of reference. Especially those that are "fuzzy" or difficult to nail down. The brain and the atom are not fully understood, but by comparing functions, structures ....

Middle of Essay
.... interference patterns of light. The third major requirement is utter stability and freedom from vibrations. As for producing an actual hologram, here is described a two-beam transmission holograph. (So named because viewing it requires shining the same coherent light back through it) The laser is placed on a platform in the sand and a mirror directs the light diagonally across the table. A beamsplitter divides the beam into two parts. One goes to a mirror that directs the light through a spreading lens onto the photographic plate at an angle. The other beam is bounced off a mirror and through a spreading lens onto the object to be holog ....