People haven't changed all that much in a thousand years, the 83-year-old gentlemen with square shoulders was saying, but startling changes have come in the field of science.

And Bern Dibner seemed fairly and reasonably proud to show guests his collection of landmark scientific books last night at the Museum of History and Technology, where a selection of 35 mastersworks will be displayed in glass cases through June 6.

Roger Kennedy, museum director, went up to one fellow, bent double peering at a page about ostriches (for the collection includes works on zoology, botany and other sciences than mathematics and physics) to say he had been chewed out by some irate person for having the books in cases so low:

"But you'll agree it's easier for you to bend down to see them than for a person in a wheelchair to stand up."

Dibner said he had come to America from the Ukraine at the age of 7. He might have said, though he didn't, that he later attended Brooklyn Polytechnic and started working in the electric power industry. While in Cuba on a job he began to think of new solutions to the problem of electrical connectors for branching circuits from main power lines.

He patented these and manufactured them, founding the Burndy Corp., which now has 27 plants and makes connectors for hydroelectric systems, wristwatches and all sorts of things in between.

"I am proudest of having served my country in World Wars I and II," he said, and it seemed to him that least he could do was give the cream of his book collection to the nation. He gave 10,000 volumes in 1974.

A trustee of the collection that still remains (there are an additional 30,000) at Norwalk, Conn., George Szabad, observed:

"Of course this [gift to the Smithsonian] was Silvio Bedini's idea. I did not have the imagination to think of it myself. When Silvio first suggested the very cream of the collection should come to the Smithsonian, a lot of us bristled. But of course Silvio was right."

Bedini, now the Smithsonian's keeper of rare books, had been in the midst of telling a small group about Pope Leo X's elephant ("a gift of the king of Portugal and the pope loved the beast, and unfortunately a rhinoceros was sent, too, but drowned on the trip, so they had him stuffed and sent along to the Vatican. This elephant epitomized the golden Renaissance, of course. Now you won't believe this curious fact, but the truth is --").

Bedini is frequently in the midst of some utterly unbelievable tale, invariably true, but he did pause at Szabad's praise to shrug off his own part in acquiring the rare books:

"The main thing, the thing that really operated, was Dr. Dibner's patriotism and old-fashioned sense of responsibility to the country. The Smithsonian is a national institution, perfect for his collection, so there you are."

"Well," someone suggested, "the Library of Congress or a great university might be an equally appropriate place."

Perish the thought, Bedini's expression showed.

Among the 35 treasures on display, with captions explaining them, are Copernicus' "De Revolutionibus Orbium Coelestium"; Galileo's "Sidereus Nuncius Magna"; Newton's "Principia"; and Darwin's "Origin of Species."

It was only in his middle age that Dibner began his serious collecting of science volumes, and entered into the joys of a scholar and bibliophile.

As often happens, his passion was born of skepticism, especially about Leonardo. It seemed to him preposterous that Leonardo was treated virtually as a god, and Dibner set out to uncover some of the baloney in Leonard-worship.

That was in 1929. A half-century later he says:

"I'm still finding fresh ideas" in Leonardo. Leonardo, he was obliged to conclude, dealt with 21 of the 22 categories into which the elements of machinery fall. (He missed rivets, probably because he saw nothing fascinating about them).

But Dibner was not a book collector until 1936 when he bought (on a vacation to Switzerland) a copy of Leonardo's "Treatise on Painting," Vol. i. Even that did not greatly convert him from a normal fellow into a bibliophile. The culprit was Vol. II which he acquired a few months later in Italy. After that the fat was in the fire, and Dibner did not rest until he had 40,000 volumes dealing with many fields of science.

Dibner's collection had grown so important, in the great basic books of science, that in 1964 he built a library at Norwalk to house them, and in which scholars could consult them. (There had been a time, during Dibner's collecting mania, when piled books made it hazardous to walk through the corporate headquarters).

The Smithsonian magazine once observed that early science books are rare partly because they were used right in the laboratory, peculiarly prone to damage from things blowing up (a thing that used to happen before techniques became perfect).

Dibner made a catalogue of 200 books as landmarks in scientific work, assigning each one a number. His catalogue was called Heralds of Science, and H.S. numbers are now widely used. The present exhibit marks the 25th anniversary of that catalogue.

Also displayed is the first book in English on electrical theory, by Queen Elizabeth's doctor, William Gilbert. A landmark book on anatomy, by the 16th-century investigator, Vesalius, along with Harvey's book on the circulation of the blood.

Fuch's great 16th-century herbal is there, including such astonishing New World plants as corn and pumpkins. A book from the 1400s by Brunschwig concerns itself with chemistry and drugs, cheek by jowl with books by Curie and Einstein, and a laboratory microscope used by Pasteur.

Along the way Dibner branched off to write a book, "Moving the Obelisks," about the engineering task of moving the obelisk into position in St. Peter's Plaza, a Roman understanding of 1586. Hundreds of workmen were involved and ropes and pulleys without number. At one point the rigging seemed likely to fall until an inspired bystander hollered "water on the ropes" -- good advice which was taken by the engineers in charge. The ropes tightened and all was well.

In science, as in engineering, as in everything else, you never know when a mere bystander may have a great and dandy notion.