model is so will our work approximate; and although we may go on
approximating _our_ ideal forever, we can never hope to reach that which
has been set for us by the great Master Workman.

* * * * *




[JOURNAL OF GAS LIGHTING.]

PHOTOMETRICAL STANDARDS.


In carrying out a series of photometrical experiments lately, I found that
it was a matter of considerable difficulty to keep the flames of the
standard candles always at their proper distance from the light to be
measured, because the wick was continually changing its position (of
course carrying the flame with it), and thus practically lengthening or
shortening the scale of the photometer, according as the flame was carried
nearer to or farther from the light at the other end of the scale. In
order, therefore, to obtain a correct idea of the extent to which this
variation of the position of the wick might influence the readings of the
photometer scale, I took a continuous number of photographs of the flame
of a candle while it was burning in a room quite free from draught; no
other person being in it during the experiment except a photographer, who
placed sensitive dry plates in a firmly fixed camera, and changed them
after an exposure of 30 seconds. In doing this he was careful to keep
close to the camera, and disturb the air of the room as little as
possible. In front of the candle a plumb-line was suspended, and remained