This article was written as if this was a newly discovered technology. I have been using an electric shaver with induction recharging for years.

Mike York
Phoenix, Ariz.

The ability to project electrical power some distance suggests a possible method to detonate or disable improvised explosive devices.

Josef Heit
Webster, N.Y.

Several readers pointed out that wireless induction already powers various devices, such as cochlear implants. However, Aristeidis Karalis of the Massachusetts Institute of Technology (MIT) responds that, to the authors’ knowledge, all previous applications used induction at distances not substantially larger than the size of coils involved. Second, the MIT invention could in principle shut down the electronics of a bomb detonator, but at no greater a distance than a few meters. —D. Castelvecchi