Letters to the Editor

19161

You are usually pretty good at explaining things to those of us outside the hard sciences, but the speed of gravity? Speed of light OK, but what is the speed of gravity? Robert L. SchragNorth Carolina State UniversityRaleigh, N.C. An object with mass creates a gravitational field around itself. Imagine that the object moves; then, […]

19160

I found the “stats” about blood donors and patients in this article misleading, with the implication that 8 million volunteer donors are more than enough for 4.5 million patients. A comparison of how many people donate blood during their lives and how many people need blood donations during theirs might have been more informative.