Irving Geis, 88, illustrator of obscure scientific concepts. Geis, as illustrator for Scientific American from 1948 to 1983, helped readers understand and visualize such topics as continental drift, DNA's double helixes and space exploration. He illustrated textbooks on immunology, chemistry and biochemistry and did the artwork for the popular book "How to Lie With Statistics." Geis regularly exhibited his portraits of molecules around the country. In 1987, he won a Guggenheim Fellowship to create an artistic archive on molecular structures. During World War II, Geis was an art director and chief of graphics for the Office of Strategic Services. On July 22 in New York of a cerebral hemorrhage.