What chance laboratory occurrence led to the invention of the microwave oven?

Cooking food with microwaves was discovered by Percy Spencer while building magnetrons for rader sets at Raytheon. He was working on an active radar set when he noticed a strange sensation, and saw that a peanut chocolate bar he had in his pocket started to melt. Although he was not the first to notice this phenomenon, as the holder of 120 patents, Spencer was no stranger to discovery and experiment, and realized what was happening. The radar had melted his candy bar with microwaves. That was a quote from the Wikipedia article. A link is provided.