Editing Pytheas (section)

== On the tides ==
Pliny reported that "Pytheas of Massalia informs us, that in Britain the tide rises 80&nbsp;cubits."<ref>''Natural History'' [https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0137%3Abook%3D2%3Achapter%3D99 Book II Chapter 99]</ref> The passage does not give enough information to determine which cubit Pliny meant; however, any cubit gives the same general result. If he was reading an early source, the cubit may have been the [[Cubit#Other systems|Cyrenaic]] cubit, an early Greek cubit, of 463.1&nbsp;mm, in which case the distance was {{convert|37|m|ft}}. This number far exceeds any modern known tides. The [[National Oceanography Centre]], which records tides at tidal gauges placed in about 55&nbsp;ports of the UK Tide Gauge Network on an ongoing basis, records the highest mean tidal change between 1987 and 2007 at [[Avonmouth]] in the [[Severn Estuary]] of {{convert|6.955|m|ft|abbr=on}}.<ref>{{cite web | title=Harmonic Constants | publisher=National Oceanography Centre | date=3 July 2012 | url=http://www.pol.ac.uk/ntslf/constants2.php | url-status=dead | archive-url=https://web.archive.org/web/20120703100723/http://www.pol.ac.uk/ntslf/constants2.php | archive-date=3 July 2012 }}</ref>

The highest predicted spring [[tide]] between 2008 and 2026 at that location will be {{convert|14.64|m|ft|abbr=on}} on 29 September 2015.<ref>{{cite web | title=Highest & lowest predicted tides | publisher=National Oceanography Centre | date=3 July 2012 | url=http://www.pol.ac.uk/ntslf/hilo.php?port=avonmouth | url-status=dead | archive-url=https://web.archive.org/web/20120703100710/http://www.pol.ac.uk/ntslf/hilo.php?port=avonmouth | archive-date=3 July 2012 }}</ref> Even allowing for geologic and climate change, Pytheas' 80 cubits far exceeds any known tides around Britain. One well-circulated but unevidenced answer to the paradox is that Pytheas was referring to a storm surge.<ref name=Tozer2>{{cite book|last=Tozer|first=Henry Fanshawe|title=A History of Ancient Geography|year=1897|location=Cambridge|publisher=Cambriddge University Press|pages=225|url=https://archive.org/details/b24876628/page/225/mode/2up/search/storm}}.</ref> Despite the modern arguments, the fact remains that Pytheas experienced tides that exceeded by far the usual tides in the Mediterranean, and particularly those at Massilia.

Matching fragments of [[Aetius (philosopher)|Aëtius]] in pseudo-[[Plutarch]] and [[Stobaeus]]<ref>{{cite book|title=Doxographi Graeci|url=https://archive.org/details/doxographigraec01dielgoog|editor-first=Hermann|editor-last=Diels|editor-link=Hermann Diels|publisher=G. Reimer|date=1879|location=Berlin|pages=[https://archive.org/details/doxographigraec01dielgoog/page/n397 383]|language=grc}} [https://archive.org/details/doxographigraec01dielgoog <!-- quote=Doxographi Graeci. --> Downloadable Internet Archive]. Diels includes two matching fragments of [[Aetius (philosopher)|Aëtius]]' ''Placita'', one from Pseudo-[[Plutarch]] ''Epitome'' Book&nbsp;III Chapter&nbsp;17 often included in ''[[Moralia]]'' and the other from [[Stobaeus]]' ''Extracta'' Book&nbsp;I Chapter&nbsp;38&nbsp;[33].</ref> attribute the flood tides ({{lang|grc|πλήμμυραι}} ''plēmmurai'') to the "filling of the moon" ({{lang|grc|πλήρωσις τῆς σελήνης}} ''plērōsis tēs sēlēnēs'') and the ebb tides ({{lang|grc|ἀμπώτιδες}} ''ampōtides'') to the "lessening" ({{lang|grc|μείωσις}} ''meiōsis''). The words are too ambiguous to make an exact determination of Pytheas' meaning, whether diurnal or [[Tide#Range variation: springs and neaps|spring and neap tides]] are meant, or whether full and new moons or the half-cycles in which they occur. Different translators take different views.

That daily tides should be caused by full moons and new moons is manifestly wrong, which would be a surprising view in a Greek astronomer and mathematician of the times. He could have meant that spring and neap tides were caused by new and full moons, which is partially correct in that spring tides occur at those times. A gravitational theory (objects fall to the center) existed at the time but Pytheas appears to have meant that the phases themselves were the causes (αἰτίαι ''aitiai''). However imperfect or imperfectly related the viewpoint, Pytheas was the first to associate the tides to the [[Moon#Tidal effects|phases of the moon]].