In a message dated 6/5/00 2:23:37 PM Eastern Daylight Time, [EMAIL PROTECTED] writes:
> So far so good, but now for the third control - a swivel mounting which > allows the entire dial to be rotated about a vertical line running through > the centre of the sphere. Well, I will hazard a guess. Rotation about a vertical axis, as you describe, would be a nice feature for fine-tuning alignment of the dial in a north/south meridian. As you know, the dial would be turned so that it read noon at solar noon. It should then be in north/south alignment, and at that point I would expect the rotation to be locked down by tightening the carriage bolt. I see no reason for leaving this axis loose once it has been set. As a minor aside, I should state that for most dials this would be the way to find north. But for this dial, where the equatorial band can be rotated as well, this method works only if the band is set for its time zone meridian. For example, if the band has been shifted 8 minutes to account for placement 2 degrees away from the meridian, this alignment method will be inaccurate. In this case, you would find north by using the method just described with the but set the dial for 11:52 (if you are EAST of the meridian) at solar noon. As another minor aside, although this technique for finding north is commonly known among dialists, does anyone know a nice technique for aligning the dial for the proper latitude. That is, adjusting the north/south tilt of the dial until the stile is in perfect alignment with the celestial pole? I don't mean just elevating the stile to an angle measured to be equal to your latitude, but actually taking time measurements off of the dial, and then determining how to fine tune the adjustment to get it exactly right. I worked out a method a year ago, which I'll have to look up, but as I recall, it may have involved a little bit of math. In the meantime, do we have any takers? Bill Gottesman Burlington, VT 44.4674 N, 73.2027 W
