008 Scientific Proceedings, Royal Dublin Society. 
magnitude star it must have been more than 10,000 times brighter 
than the Sun. 
The most serious question is: Would the nebula be capable of 
reflecting enough of the light from the Nova to be visible to us? 
If we take — as the ratio of the light of a lst magnitude 
star to that of the Sun, then the edge of the nebula being 430 
times closer to the Nova than the Earth the light it would receive 
430? 1 
2 a oe 
would be 430°, OF 10" ° 970500 
Taking Young’s estimate of the light of the full Moon as 
of sunlight. 
equal to of that of the Sun, the nebula would receive about 
1 
600000 
2°2 times the light of full Moon. 
The nebula being of finite area its intrinsic brilliancy would 
not be reduced by its distance from the Harth, so that allowing 
for the “albido” of the nebula, or the amount of light its 
particles are able to reflect as one-half, its particles ought to be in- 
trinsically as bright as the Moon. SButthe particles of the nebula 
are evidently widely separated in space from each other, as the 
nebula seems very transparent. We, therefore, would not probably 
receive anything like the light of moonlight. The intrinsic 
brilliancy of the nebula, from the very long exposures required to 
photograph it, is certainly not greater than an 18th magnitude 
star ; and as the light of the Nova was about a Ist magnitude one, 
the amount of light reflected from the nebula seems to be only 
, and if we take the light of the Nova at its 
canal ee 
a 6310000 
: ‘ LL 
maximum as equal to 0°2 magnitude the ratio becomes 18180000 
of the light it received from the star. 
I consider, therefore, that we have very strong grounds for 
thinking that the nebula is able to reflect enough light to become 
visible to us, and that this apparent expansion of the nebula is 
entirely due to the advance of the wave of light sent out by the 
outburst of the star. 
It thus becomes possible for the first time to determine the 
distance of a star whose parallax is unknown. 
