Position Finding with Spirit Level

Extract

The use of the Sun's shadow is a very old method for position finding. It is easy to adapt a small spirit level to produce a shadow on a millimetre scale which will give results of sufficient accuracy to add to the interest in learning to work out position lines for the Sun; less accurately for the Moon. Schools might find this useful for theoretical and practical classes.

The illustrations explain the principles involved and the constructional details. With practice it is fairly easy to set the style to the height necessary to give a clear shadow and to record its length to one tenth of a millimetre on the scale. To avoid errors of parallax in setting the style, the pinhole sight is held at the required height at the end of the spirit level opposite to the style while the latter's height is measured with the millimetre rule which should be held, vertical, about where the shadow is found to end on the scale.