''At one point, his wife nearly threw him out of the house because all he did was tinker,'' he said. After minor successes with inventions, he added, Mr. Johnson finally ''came up with one that allowed him to no longer have to work for anybody.''

It happened in 1982 while Mr. Johnson was working at home on a new kind of cooling device. At that time, refrigerators often used Freon, a gas that destroys the earth's ozone layer. He envisioned one that ran on water. It would not only be efficient but would also be environmentally friendly.

Mr. Johnson was tinkering with parts for his device when he experienced his squirt-gun eureka. He built a prototype for his 6-year-old daughter, and rave reviews from around the neighborhood convinced him that it had commercial potential.

For decades, the science of squirt guns was simple: pulling a trigger forced water in a small chamber out through a narrow opening. That principle has worked not only for water pistols but also for dispensers of perfumes, window cleaners and other household products.

Mr. Johnson's squirt gun was different. Most important, it abandoned the small water pump and made it possible to employ much more than the energy of a single finger squeeze. Instead, a child drove a large air pump repeatedly, with each stroke adding more air to produce greater compression and store more energy.

''A small kid would not have enough strength to create the level of force needed to make the gun shoot a long way,'' he recalled. ''So I had to put the energy in a little bit at a time.''

Repeated pump strokes sent air into a strong chamber filled with water. The pressure grew and grew, until a pull on the trigger unleashed torrents.