Letters from the June 12, 2004, issue of Science News

Go with the flow

In “Tales of the Undammed: Removing barriers doesn’t automatically restore river health” (SN: 4/10/04, p. 235: Tales of the Undammed), the photo comparison of the dam site is deceptive because the two photos of the same spot appear to have been taken during different seasons. Hence, the lower photo shows a scene that appears excessively desolate, but not because of the loss of the dam.

Michael C. Reed
Kalamazoo, Mich.

Yes, Sir, you did

I described everything in “Primal Progress: Pattern hunters spy order among prime numbers” (SN: 4/24/04, p. 260: Primal Progress: Pattern hunters spy order among prime numbers) almost 50 years ago in The City and the Stars (1956, Harcourt, Brace, and World). See chapter 6: “He set up the matrix of all possible integers, and started his computer stringing the primes across its surface as beads might be arranged at the intersections of a mesh. Jeserac had done this a hundred times before and it had never taught him anything. But he was fascinated by the way in which the numbers he was studying were scattered, apparently according to no laws, across the spectrum of the integers.” Elsewhere, I describe looking for prime lineups when all the integers are written in a spiral.

Arthur C. Clarke
Sri Lanka

The right light

The article “Photon Double Whammy: Careening electrons may rev up solar cells” (SN: 4/24/04, p. 259: Photon Double Whammy: Careening electrons may rev up solar cells) focused exclusively on the conversion efficiency of the solar cells. To my way of thinking, the important parameter is not output power versus input power but output power per dollar cost. The size of the arrays is generally not the deciding item. If their efficiency were only 10 percent, but they cost 10 cents a square meter, you could sell a lot of them.

Terry Klein
Troy, N.Y.