“Gatling Gun” -- an electrostatic generator introduced by Ratheon’s Macalaster Scientific Company, Nashua, N.H., creates artificial lightning for study by science students. Plastic cylinder ringed by aluminum rods rotates at high speed to build up charges of 85,000 volts that spark between balls in foreground. Unlike traditional generators of greater complexity and cost, the new Macalaster classroom apparatus is unaffected by humidity.