The Lamp Chronometer

Figure 4 represents a chamber lamp, A, consisting of a cylindrical
vessel made of tin, in the shape of a candle, and is to be filled with
oil. This vessel should be about three inches high and one inch
diameter, placed in a stand, B. The whole apparatus, of lamp and
stand, can be purchased, ready-made, at any tin-shop in London. To the
stand, B, is fixed the handle C, which supports the frame D, about 12
inches high, and four inches wide. This frame is to be covered with
oiled paper, and divided into 12 equal parts by horizontal lines, at
the end of which are written the numbers for the hours, from 1 to 12,
and between the horizontal lines, and diagonals, divided into halves,
quarters, &c. On the handle C, and close to the glass, is fixed the
style or hand E.

Now, as the distance of the style from the flame of the lamp is only
half an inch, then, if the distance of the frame from the style be six
inches, while the float that contains the light descends by the
decrease on the oil, one inch, the shadow of the style of the frame
will ascend 12 inches, being its whole length, and show by its
progression, the regular increase of the hours, with their several
divisions.

You must be careful always to burn the same oil, which must be the
best; and the wick must never vary in size; if these precautions are
not attended to, the dial never can be accurate.

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