A Shaken World "Seismic Shift" [September] was very interesting, particularly in light of the recent attacks on New York City and Washington, D.C. I was impressed by the extent of information obtained from the seismic record of the Kursk explosion. I would be very interested in learning about the kind of seismic data and information that was obtained from the terrorist attacks. I am also wondering if this technology is being used (or has been used in the past) to gather information on terrorist organizations.
Steve BrowningSan Francisco, California
Seismologist Terry Wallace responds: Governments have long used seismology to investigate explosions, whether accidental or intentional. The U.S. government is also one of several that operate seismic stations to monitor nuclear-weapons testing. These same stations have been used to investigate other phenomena of military significance. In the case of the World Trade Center attack, the horrific events were recorded by stations that were installed to monitor the earthquake activity of New York State. Several Web sites, including www.geo. arizona.edu/geophysics/faculty/ wallace/WTC, give the seismological details. Seismology did not add much to our understanding of the attack but did help discount rumors, such as claims that there were separate explosions beneath the WTC towers that helped cause the buildings' collapse.
Curtain Going Up David Schmidt's 1.5 trillion calculations on a $28,000 software package ["The Tornado in the Shower," R&D;, October] still don't negate the fact that until the water reaches a temperature significantly above that of the room, a shower curtain will not billow inward at the bottom, as it would if the motion was caused by some sort of vortex formed by the falling water droplets, regardless of temperature. It appears that Occam's razor nicely shreds Schmidt's solution to the shower-curtain conundrum. The simpler explanation is this: As it falls, heated water imparts its heat to the surrounding air. This causes the air within the shower stall to rise, causing a chimney effect in which colder air rushes in at the bottom to replace the warmer air escaping out the top of the stall, forcing the bottom of the curtain inward by its movement. It took several cold showers to confirm this phenomenon, but I feel it was worth it.
Dale WciselDavison, Michigan
David Schmidt responds: The heat of the shower may add an additional force to pull the curtain inward, but many shower curtains pull in with a cold spray. Thus there must be a force attributable only to the motion of the water and the air. The beauty of this problem is that we can all look in our own showers and form our own opinions, but it is important to remember that all showers are different. Depending on the spray, the curtain, and the size of the shower stall, the curtain may behave differently. Also, readers should know that I did not spend $28,000 for the purposes of this calculation. I already had the software from previous work.
Hook, Line, and Sinker "The Most Important Fish in the Sea" [September] is based on two untruths—that the fishing effort "has escalated in recent decades," resulting in the overfishing of menhaden, and that the industry is not regulated. According to NOAA Fisheries-Beaufort, the average annual fishing effort has declined every decade since 1959. Less effort leads to lower catches, which then creates a projection of a lower menhaden population. The Atlantic menhaden is generally caught within three to four miles of the coast; many of these waters are now closed to menhaden fishing. Once there were plants from Florida to Maine; now many of these states do not permit menhaden fishing. Several states effectively prevent menhaden fishing through restrictions. What stronger regulation is there than not permitting fishermen to go where the fish are?
Robert W. Smith Former President, Seacoast Products and Ampro Fisheries—Weems, Virginia
H. Bruce Franklin responds: My article claims neither that the menhaden fishing "effort" has escalated nor that the fishery is unregulated. Why has the menhaden catch been steadily declining? Why have many states banned or restricted the fishery? The answer to both questions is simple: Atlantic menhaden are evidently crashing. Why is the industry not fishing New England waters? Because adult menhaden schools have not been seen north of Cape Cod since 1993. As my article states, the decline in menhaden is already dangerously damaging the ecosystem, which is why so many experts are warning that we must act now to save the species.
More Dirt on DustThe Secret Life of Dust by Hannah Holmes, from which our September feature "Stardust" was excerpted, is available at bookstores, online booksellers, and from John Wiley & Sons (800-CALL WILEY, or www.wiley.com).
Errata The astronomer identified as William Herschel on page 76 of the October issue is his son, astronomer John Herschel.
