Sundials that set off guns, lights - whatever on time!

User Rating: / 0
PoorBest 

Sundial Alarms       PDF       Print       E-mail
Written by Administrator   
Thursday, 05 March 2009 16:31

The inspiration for the Sundial Alarms came from a popular nineteenth century sundial called the noon cannon, like this example in the Czech Republic. It fired a miniature black powder cannon at solar noon by focusing sunlight on the touch hole of the cannon. It was hard to set and only had one chance a day of going off. Modern Sundial Alarms can be set to go off at anytime the sun is shining.

Once set up correctly the Sundial Alarm should function accurately all year. The alarm and lens holder is rotated around the central arm to set the time for the alarm--indicated on the hour dial. The alarm and lens holder is rotated around its attachment to the arm to select the date--indicated on the seasonal dial. A firecracker is placed in the holder and the fuse adjusted across the target area where the lens focuses sunlight. When the sun moves to the right position in the sky, the focused sunlight will ignite the fuse and the alarm will sound.

Brief instructions for a Sundial Alarm:

To function properly a sunny location should be selected--the sun must shine on the Sundial Alarm at the time it is supposed to go off. Remember that the sun moves throughout the day, and also changes its track across the sky seasonally. Choose a spot where there will be bright sunlight at the time you wish the alarm to sound.

First orient the Sundial Alarm to true north and level. The built-in compass will help, but it should be remembered that magnetic north is not the same as true north. Geological Survey Maps (http://store.usgs.gov/ for the U.S.) will show the local "magnetic declination" that will tell you how far from true north the compass will be. True north can also be found by using the Sundial Alarm and the corrected time. Solar time and clock time do not agree, but tables of "the equation of time" are readily available at www.sundials.org. It's easier than it sounds. After finding true north, leveling is accomplished by turning the three leveling screws until the bubble in the built-in level is exactly centered.

Next the central arm of the Sundial Alarm is pivoted along the arc until it is parallel to the axis of the earth, or pointing at the north star, if located in the northern hemisphere. The latitude of the location is the setting for the arm, and can be found on Geological Survey Maps. A protractor and a plumb bob, or a framing square, can be used to find the right angle. On certain days the Sundial Alarm itself can help you find the correct latitude setting. The seasonal dial shows the first day of each month, and the solstices and equinoxes. First set the seasonal dial to the proper day, and the hour dial to the corrected solar time. Then move the arm along the arc until the focused sunlight falls into the lens target area (where the firecracker fuse is).