62 
Proceedings of the Royal Society of Edinburgh. [Sess. 
(2) The distances between adjacent burners that correspond to the 
maximum illuminating power, and also the distances corresponding to 
inflexion points, increase with the number of burners in the group ; also, the 
maximum illuminating power decreases as the number of burners increases 
(Tables YI. and VII.). 
(3) Quantitatively, the three- and four-burner groups behave in a very 
similar manner, while the two-burner group behaves differently, suggesting 
a radical difference between a two-burner group and any other symmetrical 
group. 
(4) The effects can be explained qualitatively by assuming the operation 
of two factors, one tending to increase, the other tending to decrease, the 
luminosity ; the increasing factor is always in excess of the decreasing one 
(for distances >’8 cm.). 
(5) Suggested factors, which also explain (3), are : — 
Increasing | 
Decreasing 
(a) draught due to neighbouring flames. 
( b ) heating effect of neighbouring flames. 
(a) decrease of oxygen supply due to neighbouring flames. 
(b) combustion products from neighbouring flames. 
The expenses of these experiments were defrayed from the Tait 
Memorial Fund. 
( Issued separately December 23 , 1909 .) 
