In 1847 Thoreau left Walden Lake abruptly, and for a time occupied himself with lead-pencil making, the parental trade.
The Santa Maria mines of Sonora, Mexico, probably the richest deposits in the world, supply the American lead pencil manufacturers.
These should be wiped with a little white paint or linseed oil, and written with a soft lead pencil before the surface becomes dry.
A small column, as for example a lead pencil standing on end, or a row of pins propped up against suitable supports, or other bodies which are easily overturned, may be used as seismoscopes.
You can also make a sucking device with a modified retractable lead pencil.
