Everyone knows funk music reached its heyday in the 1970s, but even legends like James Brown and George Clinton were hard pressed to compete with funk powerhouse The Isley Brothers in 1975. The title track “The Heat Is On (Part 1 & 2),” from their record of the same name, is a hard-driving, wall-shaking revelation that takes this oft-underestimated genre to new heights. The influences of Jimi Hendrix’s guitar, Stevie Wonder’s synthesizer, and James Brown’s rhythm make this funk anthem sizzle