Let a small mould candle, when lighted, be so placed as neither to produce smoke nor require snuffing, and it will lose an ounce of its weight in three hours. Let this quantity of light produced under these circumstances, be represented by 1.00.
Then should this candle at any other time, lose more or less of its weight in three hours than an ounce, the quantity of light will be still known, because the quantity of light in a given time is directly as the weight of the candle consumed.[6]
[6] To investigate rules for this purpose, 1. Let M represent the mould candle, _a_ its distance from the wall, on which the shadows were compared, _x_ its quantity of matter consumed in a given time, (_t_) and Q the quantity of light emitted by M in the same time: 2. Let _m_ represent any other candle, _b_ its distance from the same wall, and _y_ its quantity of matter consumed, in the time _t_.
Then as the intensities of light are directly as the squares of the distances of the two candles from the wall, we have as _a_² : Q ∷ _b_² : (_b_² + Q)/_a_² = the quantity of light, emitted by _m_ in the time.
Then let us suppose that the quantities of light are directly as the quantities of matter consumed in the time _t_, and we have, As _x_ : Q ∷ _y_ : (_y_ + Q)/_x_ = the quantity of light emitted by _m_ in that time, by hypothesis.
Now, when (_b_² + Q)/_a_² (Theo. 1.) is = (Y + Q)/X (Theo. 2.) the quantities of light of M and _m_ are directly as their quantities of matter consumed in any given time.
METHOD OF INCREASING THE LIGHT OF TALLOW CANDLES, AND TO OBVIATE THE NECESSITY OF SNUFFING THEM.
Mr. EZEKIEL WALKER has shewn that, if a trifling alteration be made in the method of using common tallow candles, they will become excellent substitutes for those of wax.
A common candle, weighing one-tenth of a pound, containing fourteen single threads of fine cotton, placed so as to form an angle of 30 degrees[7] with the perpendicular, and lighted, requires no snuffing; and what is much more valuable for some purposes, it gives a light that is nearly uniform in strength without the least smoke. These effects are thus produced:
[7] Candlesticks may be made to hold the candle at this angle, or they may be so contrived as to hold the candle at any angle at pleasure.