Skip to main content

Features

The Sensing of Chemicals by Bacteria

Motile bacteria are capable of chemotaxis, or movement toward some chemicals and away from others. Chemosensors in the cell envelope can detect the chemicals and signal the flagella of the cell to respond

By Julius Adler

Subjective Contours

Certain combinations of incomplete figures give rise to clearly visilble contours even when the contours do not actually exist. It appears that such contours are supplied by the visual system

By Gaetano Kanizsa

Catastrophe Theory

Things that change suddenly, by fits and starts, have long resisted mathematical analysis. A method derived from topology describes these phenomena as examples of seven "elementary catastrophes"

By E. C. Zeeman

Opals

What makes these gems sparkle with flecks of pure spectral color when they are rotated in white light? The answer has been found in the optical behavior of regularly stacked tiny spheres of silica

By P. J. Darragh, A. J. Gaskin and J. V. Sanders

The Analysis of Materials by X-Ray Absorption

Tiny wiggles in the characteristic X-ray-absorption "signature" of an atom embedded in a solid can now be interpreted to provide clues to the exact spatial arrangement of the neighboring atoms

By Edward A. Stern

Galileo and the First Mechanical Computing Device

It was the sector, which could be employed to solve mechanically a number of mathematical problems. Galileo devised it to attack an insoluble problem and then perceived its value for simpler ones

By Stillman Drake

The Nile Crocodile

Found both in the Nile and in most other African rivers and lakes, it has a remarkably large repertory of social behavior that includes parental protection of the young

By Anthony C. Pooley and Carl Gans

Departments

  • 50 and 100 Years Ago, April 1976

  • The Science-Textbook Controversies

  • Science and the Citizen, April 1976

  • Letters

    Letters to the Editors, April 1976

  • Recommended

    Books, April 1976

  • Mathematical Recreation

    Mathematical Games, April 1976

  • Departments

    The Authors, April 1976

  • Bibliography, April 1976

Purchase To Read More

Already purchased this issue? Sign In to Access
Select Format
April 1976

See the World from a Different Perspective

Subscribe to Scientific American MIND