916 REPORT—1885. 
probable that a liquid nucleus was already formed at the period of separation of the 
earth and moon systems, so that the tangential motion of the exterior nebulous 
mass surrounding it must be taken into the relative inertia of the denser centre. 
Therefore the present velocity of the earth’s rotation becomes quite rational, allow- 
ing this deduction from its former nebular velocity, assuming this has remained a 
constant on the conditions proposed, according to the hypothesis of Laplace. 
9. On a Galvanic Battery. By C. J. Burnett. 
MONDAY, SEPTEMBER 14. 
The following Reports and Papers were read :— 
1. Report of the Committee on Standards of White Light. 
See Reports, p. 61. 
2. Photometry with the Pentane Standard. 
By A. Vurnon Harcourt, W.A., F.B.S. 
At Southport two years ago the author exhibited and described a lamp fed 
with a mixture of gaseous pentane and air which gave constantly when its flame 
was maintained at a height of 24 inches (65°5 m.m,) the light of an average sperm 
candle. Various improvements in the lamp have been made since that date. The 
narrow tube whose diameter determines the quality of the gas burnt forms the 
through-way of the plug of a stopcock at the bottom of the siphon, and thus its 
freedom from obstruction can be verified at any moment. A metal cylinder con- 
taining an arrangement of rack and pinion by which the wire above the flame can 
be adjusted to any desired height has been placed round the burner, and upon this 
when the flame is exposed to draughts stands a glass chimney partially closed above 
and below by a perforated metal plate. Thus protected, the flame of the lamp is 
much steadier than the flame of the candle. 
The loss of light due to a thin cylindrical chimney of clear glass has been found 
by placing such chimneys round a small glow lamp, through which a constant cur- 
yent was passed. It amounts to about 1 percent. A greater absorption of light, 
amounting to 6 per cent., occurred with an equally clear chimney of thicker glass. 
By adjustment of the size and number of the holes in the plates below and above 
the chimney, the height and brightness of the flame can be made the same when 
the chimney is used and when it is not. 
The relation between the height of the flame of pentane gas burning from a 
easholder and the light emitted has been determined. From a height of 715 m.m., 
at which the flame gives the light of 1-2 candle, down to a height of 35:5 m.m., at 
which the light is that of 0°3 candle, every millimetre of height corresponds to a 
light of ‘025 or 3, of a candle. Measurements of the light of gas and oil flames 
ranging from 900 to 2,500 candles were made at a distance of 50 feet in the photo- 
metric gallery at the S. Foreland, the pentane burner being fixed at a distance of 
one or ,/2 foot from the illuminated paper, by adjusting the height of the flame 
till equal illumination was obtained, bringing down the platinum wire till it touched 
the tip of the flame, lowering or extinguishing the flame, and reading on a scale of 
millimetres the height of the wire above the burner. 
For testing lighthouse burners with a Bunsen photometer the pentane lamp was 
used either at its normal height of 63-5 m.m. or, when distant lights had to be 
measured, with a shorter flame. The relation between the height of flame and light 
of the lamp has been determined for a range of 30 m.m. 
Lastly, the effect of variations of atmospheric pressure upon the pentane flame 
