Front the end of the nineteenth century, communications engineers developed a new approach to the use of mathematics, initially through the use of phasors, and then through increasingly sophisticated time- and frequency-domain modelling. The abstraction of system components led to a « metalanguage » in which the manipulation of circuit configurations and other symbolic representations became a natural consequence of -and, increasingly, an alternative to- the mathematics. Systems ideas that originated with communications engineering were extended to other domains such as control engineering, and a highly significant synergetic relationship developed between the mathematical modelling of systems and components, the design of instrumentation, the development of the analogue computer, and the design of devices and systems. The history of this approach appears not to have been researched by historians of either technology or mathematics.