Sympathetic attractions

Most prehistoric shamans were concerned with using magic to help with the success of the hunt. They painted pictures on the walls of caves of the types of animals that the hunters desired. It is believed that this practice was a type of sympathetic magic, based on the idea that like attracts like. By painting a picture of a deer or a bison, the prehistoric shaman hoped to draw the actual animal to the hunter. Perhaps he or she believed that the picture captured the animal s soul and that the body would follow. 

In addition to electrostatic, exchange, and induction (a.k.a. deformation) energy, the fourth principal contributor to the interaction energy is the so-called dispersion energy [39]. This quantity is closely related to the London forces that are well known from freshman chemistry texts that originate from instantaneous fluctuations of the electron density of one molecule, which cause a sympathetic series of instantaneous density fluctuations in its partner. Dispersion, by its very nature, is attractive. In terms of ab initio molecular orbital theory, the dispersion energy is not present at the SCF level, but is a byproduct of the inclusion of electron correlation into the calculation. The reader is hence alerted to the fact that calculations that do not include electron correlation (and there are many such, particularly in the early literature) cannot be expected to include this fourth, and sometimes very important, component of the noncovalent force. 

Scheele in 1773 noticed that when a drop of blue solution was put on paper, the blue colour precipitated and a clear ring of water spread from the spot the blue particles are attracted by the tiny capillaries (Haarrohrlein) and it is doubtful if the mechanism of dyeing can be explained chemically. Bergman says Scheele discovered that writing with cobalt chloride (sympathetic ink) became blue in air dried by quicklime or concentrated sulphuric acid in a flask, as well as on heating. 

The military market is particularly attractive as it often can be a sympathetic early adopter of new technologies, willing to accept high prices and limited performance if other application-specific requirements can be met (such as low noise, low thermal signature, long duration both in oper-... 

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