An example of an analogy used in a popular science book:
"Each cell contains in the its interior a small spherical body known as the nucleus, which is formed by a fine network of the substance known as chromatin. It must be noticed here that various parts of the protoplasm forming the body of the cell have under normal circumstances equal optical transparencies so that the structure cannot be observed simply by looking at a living cell through a microscope. In order to see the structure we have to dye the material of the cell, taking advantage of the fact that different structural parts of the protoplasm absorb the dyeing materials in various degrees. The material forming the network of the nucleus is especially susceptible to the dyeing process, and appears clearly visible against the lighter background.
You can see a similar method by writing something on a piece of paper with a wax candle. The writing will be invisible until you try to shade the paper with a black pencil. since the graphite will not stick to the places covered with wax the writing will stand out clearly on the shaded background."
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
Read examples of scientific analogies
