LettersDiscussion and Correspondence FILTERED AIR By Alexander McAdie See allHide authors and affiliations Science 28 Jul 1922:Vol. 56, Issue 1439, pp. 108DOI: 10.1126/science.56.1439.108 Alexander McAdie Find this author on Google Scholar Find this author on PubMed Search for this author on this site Article Info & Metrics eLetters PDF This is a PDF-only article. The first page of the PDF of this article appears above.