On Thanksgiving Day, 1904, grain harvester manufacturer Benjamin Holt tested a new earth moving machine on a farm near Stockton, Calif.

By the time he finished his experiment, more than just earth moved.

The invention of the diesel-powered traction machines that could move over land too soft to support horsedrawn or wheeled tractors caused a revolution not only in the farming business but in the construction and military businesses as well: Holt's track-drive principal was applied later to everything from bulldozers to the World War I military tank.

In celebration of the 75th anniversary of that tractor, the Smithsonian Institution's Museum of History and Technology put on display last week a 1929 Caterpillar tractor called the "cat 10."

It was a merger of the Holt Manufacturing Co. and the Best Tractor Co. in 1925 that created the Caterpillar Tractor Co., which is today the largest crawler-tractor manufacturing firm in the country.

The "Cat 10" on display is a gift from George E. Logue of Trout Run, Pa., a businessman who has collected over 50 antique pieces of caterpillar equipment since he first developed a passion for them living on a farm at age five.

"It's a totally American invention," Logue says of the Caterpillar tractor. "What would transportation be without the bulldozer? What would our roads, shipyards, airports, anything be like? It all has to start with the bulldozer."

The "Model A" of the tractor business, the "Cat 10" was the smallest ever built by Caterpillar. Nearly 5,000 were produced between 1928 and 1931, selling for about $1,100.

But that tractor represents only one of the many manifestations of Holt's dream machine.

There are millions of tractors on farms across the nation today. The track-type tractor has more than doubled farm output per man-hour since they were first put into mass use 50 years ago.

Militarily, they were first used by the Allies in 1916. In fact, the word "tank" originated because of the way in which the new weapons were shipped overseas during the first World War.

The armor-plated machines with tractor treads considered a secret weapon. So when they were shipped they were identified only as water tanks for British troops in Egypt.

Today, tractor customers expect their vehicle to live a functioning life of about 20,000 hours: roughly the equivalent of one million miles of automobile travel, the Smithsonian claims.

Not to mention what the tractor has done for George Logue. In an interview with the local newspaper in Williamsport, Pa., he said it has "had a profound effect. My life has never been the same."

Which, by the way, is easy to believe. His facination for the Caterpillar tractor led Logue to quit what he called a "respectable, good engineering job" in 1957, to work with bulldozers full time. Despite the objections of his father, Logue began digging wells and basements with his own Caterpillar.

Today, Logue heads a $5.25 million construction business with 125 employes.

"It's kind of fun to be able to make a living at what you like to do," he says.