A tall man with a scholar's stoop, he is courtly and well-spoken. His eyes, beneath white bushy brows, are the color of blue sky. Cyril Stanley Smith is speaking wonderfully of Samurai swords and chandeliers, Issac Newton and the Pharaohs. The objects are lovely, anyone can see that, but Smith sees more than we do.

Prof. Cyril Stanley Smith, 75, who helped design the atom bomb, who taught for years at MIT, is not your usual scientist, nor your usual connoisseur. His exhibition at the Smithsonian Institutuin's Museum of History and Technology deals with those regions of knowledge and discovery that now are claimed by science, but once belonged to art.

"Our emphasis," says Smith, "is on the middle part of structure, that intermediate zone between the atoms and the stars. We are speaking of materials, of metals, acids, crystals, porcelain and glass. Almost all of the materials used in engineering before the present century were known in the decorative arts before 2000 B.C. It boils down to this: The discovery of new things depends less on purposeful study than on esthetic curiosity. Necessity is not the mother of invention. Necessity is only the mother of improvement."

It is called "Aspects of Art and Science." Organized with Jon Eklund, the museum's curator of chemistry, it will remain on view through August. From the show's brochure: "The message is simple: Time and time again very subtle properties of matter have been discovered and exploited by artists and craftsmen long before rigorous science even took notice of these properties, much less explained them."

When Smith discusses a 17th-century Chinese vase, his conversation journeys from volcanoes to the sun. "The Europeans were determined to make porcelains as fine as those received from China, but the process required temperatures ever so much higher than they'd achieved before. This spins off, in Europe, a whole new study of high heat. The solar furnaces were developed for just this sort of thing. The payoff came in 1790. It was then that Sir James Hail first considered that basalt might come from lava. He made basalt in his lab. The potter's curiosity provides laboratory experiments that lead directly to geological processes. Just that sort of thing happened all the time."

There are two swords in the show One, a 16th-century scimitar from the Metropolitan Museum of Art, is of "Damascus" steel. The other is a "Nippon-To" from 13th-century Japan. "With a scimitar you can cut a silk handkerchief in two. With a crusader's sword you can hack a thick limb from a tree. With this Japanese sword you can do both," said Smith. "This is the supreme state of the metallurgical art. There are nearly a million layers of metal in that blade."

"Prisms," he continued, "were being made in England centuries before Newton used them to demonstrate that sunlight is not white, but actually composed of all the colors of the rainbow. This particular set was made in Newton's lifetime.It comes from Cambridge University. Two hundred years earlier the Jesuit missionaries had taken bits of chandelier to China as presents for their hosts. The Chinese were absolutely delighted. Those prisms were far beyond their understanding of glass. It seems a fair exchange for the porcelains they gave us. After a while, everything is connected to everything else," said Smith.

The section in the show on the history of glass begins with a blue faience ankh from the tomb of Pharaoh Ththmose IV in the Valley of the Kings and takes the viewer past the prisms to an "amorphous semiconductor" of a design so new that only two have been allowed to leave the RCA Laboratories at Princeton.

A nearby case whose subject is "Etching and the Discovery of Acids" includes 5,000-year-old carnelian beads, a seashell etched with fruit juice by Arizona Indians perhaps 1,000 years ago, and a sheet of copper etched by Rembrandt. Meteorites and crystals, illustrated manuscripts, ingots and jade axes, and a dish of iron oxide - a pigment first discovered 50,000 years ago - are all in the show.

The installation was designed by Staples and Charles, Inc., a local firm. They have a lot to learn. They have chosen to display the objects on shiny metal cylinders whose reflections fill the gallery with a ceaseless visual static that distracts the viewer.