Advances in the physical sciences often foster advances in the biological sciences. In this paper I deal with just one of those many contributions and describe a trail that leads from Faraday'discovery of electromagnetic induction to a technique called transcranial magnetic stimulation (TMS), which can be used to temporarily prevent the brain from carrying out some of its normal functions. The ‘lead time’ between Faraday (1831) and TMS (1985) was over 150 years, clearly longer than any Department of Trade and Industry would like. The path shows how scientific disciplines can interact, and, in the case of TMS at least, how the scientific concepts were always ahead of the technology. Having shown how much the use of the technique owes to other strands of investigation, I outline some of the advances in understanding brain function made by using TMS, and, in particular, the improvement it makes upon electrical stimulation and studies of the effects of brain damage. Finally, I make three predictions about the contribution that the technique will make to further discoveries in the 21st century.