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These couplets capture an essential feature of an exciting concept in the physical and biological sciences: the notion that the dynamical activity we observe in many natural phenomena is a consequence of many unseen layers of movement and that this im? perceptible motion is related from one level to the next by means of a scaling factor. Swift was reflecting on a self-similarity between scales: smaller versions of what is observed on the largest scale repeating in an ever-decreasing cascade of activity at smaller and smaller scales. Processes with this characteristic are today called fractals (1). There is no simple definition of fractals, but all attempts at a simple definition incorporate the idea that the whole is made up of parts similar to the whole in some way.