Several recent developments in ink-jet printing have motivated numerous scientists to investigate the details of the breakup process of liquid jets emanating from nozzles. The entire January 1977 issue of the IBM Journal of Research and Development was devoted to ink-jet printing technology, and several of the papers were concerned with drop formation. The main concern is the control of the relatively small called spherules by Rayleigh (1896, p. 366) and drops in the recent literature. These small form when thin ligaments separate from the main at both ends (see Figure 1). In the ink-jet printer the main are supplied with a predetermined electrical charge as they detach from the liquid column. They are then deflected to a desired location by appropriately charged downstream capacitor plates. When the satellite occur they receive a relatively large charge-to-mass ratio and their resulting large deflection causes printer malfunctions. The understanding of the drop-formation process is crucial to the control and elimination of the satellite-drop problem. This article is primarily restricted to a review of those investigations that bear on this rather narrow but very difficult aspect of jet breakup. For a detailed description of the classical work on the linear capillary instability of jets the reader is referred to Rayleigh (1896, §361) and Chandrasekhar (1961, §111). A more recent review can be found in McCarthy & Molloy (1974). Only a brief summary of this classical work, as is required for background, is presented here. The early experiments ofSavart(1833) and Magnus (1855) demonstrated that a liquid jet emanating from a circular nozzle could be made to breakup in a regular manner by supplying a steady vibration to the source tank or nozzle. Rayleigh (1879) studied the linear stability of an infinitely
David B. Bogy (1979) studied this question.