How to Make an Hourglass

Long before we had electric or battery-powered clocks, people used other devices to measure time. Sundials and water clocks were two early methods used to measure the passing of time. Many scientists believe that the hourglass was invented even earlier, during the third century in Egypt. This device consisted of two hollow chambers that were connected to one another by a tiny, hollow tube or "neck." The upper chamber was filled with sand, and it took an hour for all the sand in the upper chamber to trickle down through the neck to the lower chamber, hence the name "hourglass." When one hour had passed, the hourglass could be turned upside down, and the process began all over again. In modern times, we see hourglasses used to add a decorative touch to an end table or bookcase. Sometimes we see tiny ones used to time the cooking of soft-boiled eggs or to measure the turn of a board game player. To understand this method of keeping time, you can easily build your own hourglass and test it to see the length of time it measures.

Things You'll Need

• Plastic Soda Pop Bottles Sand Duct Tape Awl Hammer Pen Knife Brick with holes Newspaper Funnel

Instructions

1. Wash and rinse two, empty, plastic, soda pop bottles of the same size and their screw-on lids. Allow the bottles and lids to dry completely overnight.

2. Place a thick layer of newspaper on a table and lay the brick on the paper. The brick should be a common house-building brick with small round holes in it.

3. Place one of the lids upside down over one of the holes in the brick. Use the awl and pierce a hole in the center of the lid. You may need to use a hammer to force the point of the awl through the plastic lid. Flip the lid over and use the awl in the same opening, making the diameter of the hole larger than the lead of a wooden pencil--nearly an eighth of an inch.

4. Use the pen knife to scrape any rough edges off the perimeter of the hole in the lid. Place the small end of the funnel inside the top of one of the bottles. Pour clean, fine sand into the funnel until the bottle is about two-thirds full. Remove the funnel and screw the cap with the hole on the bottle.

5. Place the empty bottle upside down on the lid of the sand-filled bottle. Ensure that the necks of the bottles are aligned; use duct tape to wrap around the juncture of the two bottles. Wrap the tape carefully and firmly around at least twice. Gently try to pull and twist the bottles. If they move, you need to wrap more tape around the bottle necks.

6. Turn the whole assembly upside down carefully and watch the sand trickle down through the hole in the lid into what was once the empty bottle. If you observe the second hand on a watch from the time the sand starts to flow downwards until the top bottle is empty, you will know how much time your hourglass measures. Instead of an "hour" glass, you may have a "four minute" glass.

Tips & Warnings

• If you do not have clean, fine sand, you may use table salt. If the sand does not flow smoothly through the hole in the lid or appears to stop, you may need to disassemble the whole hourglass and make the hole in the lid larger by using an electric drill. If you wish to keep the hourglass for a long time and use it often, take it apart and use superglue to glue the lid to the sand-filled bottle, then glue the empty bottle to the top of the lid and rewrap with duct tape.

• Young children should be supervised when making or using the hourglass so they do not hurt themselves with the tools or swallow a lid or sand.