THE SPRING CONSTANT OF A SINGLE POLYMER CHAIN has been measured by researchers at the Niels Bohr Institute in Denmark (Henriette Jensenius, henry@fys.ku.dk). A measure of the stiffness of a spring or spring-like object, the spring constant has previously been determined for long polymers such as DNA molecules, but not for smaller polymers which are tens or hundreds of times shorter in length and much softer. In the present experiment, a micron-size bead in water spontaneously tethers itself to a glass plate by means of a polystyrene chain with a length of about 50 nanometers. By monitoring the distance between the bead and the plate, the researchers then studied the spring-like behavior of the polymer chain as it stretched and compressed in the fluid solution. For polymers cross-linked with some additional scaffolding, the researchers measured a spring constant of 1.5 x 10^-3 N/m. For non-cross-linked chains, the researchers measured a value of 2.5 x 10^-4 N/m, larger than expected by theory. For comparison, a Slinky has a spring constant of 1 N/m, and an atomic force microscope's cantilever, the plank-like structure whose tip scratches the surface of the sample to be imaged, has a spring constant of 0.1 N/m. (H. Jensenius et al., Phys. Rev. Lett., 22 December 1997.)