This thread has concentrated, (and quite rightly!), on dials that not only are marked with equal hours but show the same equal hour throughout the year. They are usually characterised by a gnomon which is parallel to the earth's axis. This 'technology' is thought to have been developed by the Arabs in the 10th Century though it may have been known as early as the 1st Century. In the literature one can read that it seems to have passed to Northern Europe around the 12th Century - so I presume that there must be some evidence for this! However I do not know of it. Certainly sundials were being used to correct mechanical clocks in the 13th Century and so one must presume that the technology was around then. Maybe we should look in museums for the earliest examples?
Not all modern dials use a gnomon that is parallel to the earth's axis but they still indicate 'equal hour time'. If you are preparing a discussion on the topic you perhaps ought to be careful as to what you mean by equal hours and mention that the term 'Equal Hours' has a very specific meaning in dialling. It isn't the case that all dials after a certain date show Equal Hours according to that specific meaning. Dials that show time by the shadow of the tip of a gnomon can also show equal hours in a day but, over the year the width between hour marks changes and a date related time scale has to be introduced. Although these hours are usually called Seasonal Hours (especially when talking about dials in olden times) they are neverthless equal in one sense. Such dials were in relatively common use in Greek and Roman times from about 300 BC and several examples exist. It is true though that the markings were not very accurate! Later we see (in Britain for example in Saxon times - AD 700 or so) dials that had a scale that was equally divided (indicating an understanding of the concept of equal hours) although the use of a horizontal gnomon meant that they certainly didn't show Equal Hours in the specific dialling sense. Therefore there are equal hours which are not Equal Hours!! Sorry if I have added confusion rather than clarity to the thread!! Patrick
