The Herschel (or, much less commonly, D-heptomino or J-heptomino) is a heptomino shaped like the lowercase letter h, which occurs at generation 20 of the B-heptomino. It evolves into two blocks, two gliders and a ship after 128 generations, and also produces a phi spark.
Herschels are a recognizable "bottleneck" stage of a very common progression of three small active objects, frequently seen during the evolution of chaotic patterns. An R-pentomino evolves after 28 ticks into a B-heptomino a dozen cells away from the starting point, plus some active trailing junk; the B-heptomino then evolves into a Herschel in another 20 ticks, while traveling another 8 cells in the same direction. 22 ticks and 5 cells later yet the Herschel evolves into a backwards escaping glider (known as the first natural glider, FNG), and a Herschel descendant that evolves into a larger explosion before settling down.
The unusual distance that R-pentominoes and B-heptominoes travel during their evolution into Herschels has allowed for the development of a growing collection of Herschel conduits, which use catalysts to modify the 128-step reaction. Instead of producing the still lifes and gliders described above, an input Herschel "bounces off" a series of eaters and other catalysts and produces a new output Herschel some distance away. In some cases, the active reaction travels directly "through" one or more transparent catalysts, destroying it completely and re-creating it in the same location several ticks later. The output Herschel can then become the input for another conduit, which may continue in the same direction or turn left or right. If it eventually forms a closed loop, the result is a Herschel-based oscillator or gun.
Most (but not all) conduits only engage the Herschel after its splitting into its final offspring and the FNG. Dealing with the latter is crucial in assembling a track from separate conduits: it is fired in a direction where it would commonly collide with a previous conduit's catalysts. Eater 5 is one of the most convenient solutions for this task.
The term "Herschel" is attributed to John Conway, who very early in the history of Life investigated the fates of all polyominoes up to at least 7 bits . The name is commonly ascribed to the Herschel heptomino's similarity to a planetary symbol ♄ erroneously attributed to Uranus (discovered by William Herschel in 1781.) However, in point of fact a Herschel closely resembles the symbol for Saturn, but bears no particular resemblance to either of the symbols used for Uranus. So the appropriate name might actually be "Huygens" -- but "Herschel" is now universally used by tradition.
- The right-hand domino of the Herschel parent can be removed, producing a 6 cell parent. The form shown is the parent produced by the B-heptomino.
- The Herschel great-grandparent is a specific three-tick predecessor of the Herschel, commonly seen in Herschel conduit collections that contain dependent conduits. In some situations it is helpful to display the input reaction in this form instead of the standard Herschel form. Dependent conduit inputs are catalyzed by a transparent block before the Herschel's standard form can appear, and before the Herschel's first natural glider is produced. This means that these conduits will fail if an actual Herschel is placed in the "correct" input location for a dependent conduit. Refer to F166 or Lx200 to see the correct relative placement of the standard transparent block catalyst. Almost all known Herschel conduits produce a Herschel great-grandparent near the end of their evolutionary sequence. In the original universal set of Herschel conduits, Fx158 is the only exception.
Generation 128 of a Herschel