Calculating the speed of light; building nuclear reactors
Faster and faster
In "He saw the light before anyone else did" [Sept. 21], Mark Weston wrote how Ole Romer, in 1676, was the first to determine the speed of light, and that Romer got the value as 130,000 miles per second. Unfortunately, Weston nowhere states the currently known "best" value of this speed, which is slightly larger than 186,000 miles per second. Thus the reader is unable to realize the wonder and skill of Romer's 1676 determination.
Weston goes on to describe the later improvements on Romer's original data which were made 30 years later and which changed the Romer observation that light crosses the Earth's orbit in 22 minutes, to a "better" value of 16 1/2 minutes. Surely that changes the determination to 130,000 x 22/16.5, equaling slightly more than 173,000 miles per second. However, Weston seems to imply that this second determination already gave the current value of slightly more that 186,000 miles per second.
Perhaps this apparent confusion is the fault of an attempt to shorten the article, which left out the key intermediate value?
Claude Kacser Rockville
Looking beyond uranium
The small, modular nuclear reactors described in "The nuke next door" [Sept. 14] do reduce greenhouse gases. But they would still rely on uranium-235, a limited resource with safety and proliferation concerns. Meanwhile, an entirely different approach would exploit U.S. national laboratory advances in the technology of particle accelerators.
This new approach is called the accelerator-driven subcritical reactor (ADSR). Proton accelerators can be used to extract energy from materials that are not capable of a chain reaction, such as the relatively abundant element thorium.
Unlike a conventional reactor, an ADSR can be immediately shut down simply by switching off the accelerator. A ton of its thorium fuel could yield as much energy as would be produced by 200 tons of mined uranium using a conventional reactor, or by burning 3,500,000 tons of coal. An ADSR can also generate power by destroying waste from conventional nuclear reactors.
Enthusiasm is growing worldwide for ADSRs. If the U.S. does not take advantage of its present lead in this technology, it is likely that we will be left behind and in the future have to buy our reactors from other countries.
Rolland Johnson President, Muons Inc. Chief science officer, Accelerator Technologies Inc.Newport News, Va.