hello every body, in an ancient book called " roret de l'horloger rhabilleur" a simple method is described for obtaining the meridian inside a room with a window facing south. First, you have to determine the meridian outside on the principle of a horizontal dial allowing reading of the solar noon time. They do it by a small vertical gnomon on top of which is placed a small disc with a pierced hole of 3mm & the disc inclination being that of the local latitude. ( of course, any existing outside dial, will do). The next step is the height determination of the second gnomon, same principle, with pierced disc, for marking of the inside meridian. So, he says, observe the shadow given by the vertical side of the window to the end of the room, & measure the distance end of the room -window. According a table given in the book, you can read the height of the required gnomon; some values: lenght: 3.9m height:1.22m, length: 4.875m height: 1.555m) This new gnomon has to be placed in front of the open window. The next day, you wait for solar noon on the outside dial, somebody pings this & somebody else marks the center of the spot on the floor on the pinging moment. This is the first point of the meridian. Obtaining the second point is done by putting a string from the center hole of the gnomon to the point marked on the floor, & letting a plumbers weight line mark near the window on the inside the second point. Reporting this floor meridian to the ceiling with plumber weight lines must be no problem. After that, you can ping other half/or hour lines, report them to the ceiling, & finally experiment with a mirror to find its position so spots coincide on the premarked hour lines. The last line is my personal comment, am I right or wrong there ? Walter 50.42.01 N 4.33.46N
