Arxiu online de la revista de la NGS <a href="http://mail.nysoclib.org/digital_archives/periodicals/National_Geographic/index/1970s/1970/270B.html">http://mail.nysoclib.org/digital_archives/periodicals/National_Geographic/index/1970s/1970/270B.html</a><br>
<br>Raf<br>