1![Microsoft Word - birchSHORTER.doc Microsoft Word - birchSHORTER.doc](https://www.pdfsearch.io/img/378a0328b29426dc813d057c8aab1058.jpg) | Add to Reading ListSource URL: web.gps.caltech.eduLanguage: English - Date: 2004-02-03 17:31:56
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2![national academy of sciences Percy williams Bridgman national academy of sciences Percy williams Bridgman](https://www.pdfsearch.io/img/36cf7422a7256f22a247a3126e6ffe9b.jpg) | Add to Reading ListSource URL: www.nasonline.orgLanguage: English - Date: 2011-11-09 13:53:24
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3![Proc. Amer. Phil. Soc., 143, [removed], [removed] Proc. Amer. Phil. Soc., 143, [removed], [removed]](https://www.pdfsearch.io/img/673b2d17cf3e3c54de318bfc446c4f5f.jpg) | Add to Reading ListSource URL: www.fas.harvard.eduLanguage: English - Date: 2004-02-03 17:31:56
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4![](https://www.pdfsearch.io/img/974666323345831f9d8ef73c74e72e4d.jpg) | Add to Reading ListSource URL: www.nasonline.orgLanguage: English - Date: 2011-11-01 17:29:18
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5![](https://www.pdfsearch.io/img/ade702266f4e24990413bcd9c95b6704.jpg) | Add to Reading ListSource URL: pdfhost.focus.nps.govLanguage: English - Date: 2008-03-18 03:15:52
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6![](https://www.pdfsearch.io/img/231264fb140a37da7c29acc398f89626.jpg) | Add to Reading ListSource URL: books.nap.eduLanguage: English - Date: 2009-06-16 14:04:21
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