i ag /. 
FN + aig 
86 W. A. Norton on Comets. 5 
morrow. ‘To what extent this vitiating action operates may be 
inferred from the fact that I have never been able to obtain from — 
the gas of our pipes an illuminating power equal to the minimum — 
of that reported by the engineer of the gas company. In my 3 
trials the power has varied from that of 13 candles down as low — 
as that of 9 candles, instead of ranging from 14 to 17 candles. 
This difference is perfectly intelligible if we assume the last 
quantities to represent the value of the gas when first made, and — 
ee 
Art. XIV.—On the Dynamical Condition of the Head of a Comet; 
by Professor W. A. Norton. : 
to vary inversely as the square of the distance from 
centre of the repelling mass. So far as I am aware, no attempt 
has hitherto been made to develope the idea of a aye ne 
condition of the head of a comet into a mathematical theory: 
based upon precise numerical laws. oe 
The hypothesis that a projectile force is in operation, combined 
with a repulsive action, or even with a gravitating force only, 
will also be briefly considered. : all 
Let us first suppose cometic matter to be expelled from # 
points of the surface of the nucleus, on the side toward the say 
and in directions normal to the surface, regarded as s 
eric 
As the nucleus is very small, in comparison with the nebulosity 
