The Internet Archive has a preservation copy of this work in our general collections.
No attention will be paid 1,0 commulll cations unless accompanied with the full name and address of the writer. Namesand addresses of correspondents will not be gi ven to in q IIi rers . We renew our request that correspondents, in referring to former answers or articles, will be kind enough to name tl.e date of ;;he paper ami the page, or the numoer of the question. Correspondents whose inquiries do not appear after a reasonable time should repeat them. It not then pub lished, they maydoi:10.1038/scientificamerican05171884-315 fatcat:36o5hw7dtbenboitduhbnsjd7m