Click on file es.pdf and open the result with Adobe
Acrobat reader. The reason I'm using this format is that
I feel it would be useful to be able to exchange graphic
materials in this group from time to time. I could
attach the document (which is less than 10 k) to this
message, but a significant fraction of correspondents
seems to have difficulty translating the result of such
an operation. I will be glad to e-mail the file to
anyone who requests it.
I will reveal my simple resolution of the problem,
which can be understood using high school physics, if
there is sufficient interest in it in the group.