Hello Sara , even if late I try to write some considerations regarding your message (5/1/2003)
Altitude sundials . An altitude sundial must always have a movable element with the possibility to be revolved around the local vertical direction. This element can be or the dial surface or the gnomon . For example : in the ancient Arabic sundial Hhafir it is the horizontal plane that can rotate around its vertical axis; in the shepherd' dial it is the cylinder ; in some cylindrical dials on column it is an horizontal pole (the gnomon) ; in the hat cylindrical sundial the gnomon is a disk that can be imagined as formed by infinite poles. All the ring dials - and the universal ring dial - are therefore altitude sundials. For this reason I think that the scaphe is not an altitute sundial (the shadow point is known if two coordinates of the Sun are known). In my opinion all the altitude sundials are self orienting. In an azimuth sundial the gnomon, that casts the shadow, must be a vertical element or pole whose shadow cuts a set of daily lines. In an horizontal analemmatic sundial these daily lines are reduced to single line moving the foot of the pole. For example a Lambert sundial and an analemmatic drawn on plane not horizontal are not azimuth sundials. I think that pin-gnomon dial cannot be include among the azimuth dials. I have some difficulty to express an opinion on the dials that you list, because I don't know them (magnetic azimuth--particular ;magnetic azimuth and universal multiple-faced ;Bloud-type diptych ) I think that "the horizontal (or vertical) pin-gnomon--e.g. to sundial with to vertical-(horizontal)-stick gnomon ." cannot be considered an azimuth sundial. Just a word on the sundials that mark only one hour - usually the noon - as those in the great churches, the cannon dials or many vertical dials. In this case since we can read the time only when either the azimuth or the hour angle becomes zero, I think that thay can be classified either as azimuth or directional (hour angle) : perhaps they deserve a peculiar classification :-) I have not found in your list the bifilar sundials; those with more gnomons; the reflection sundials (with mirror) and the moon dials. Best regards Gianni Ferrari 44° 39' N 10° 55' E Mailto : [EMAIL PROTECTED] -
