500 
Proceedings of the Eoyal Society 
electric light, by adapting to it more fully the condensing system, 
now largely employed on the Scottish coast, both for flashing and 
fixed lights. This system has been employed for the new electric 
group flashing light for the Isle of May, in connection also with a 
mode which I proposed of dipping the rays below the horizon on 
the occurrence of haze or fog, so as at such times to increase the 
power of the light at short distances from the lighthouse, where 
alone it is likely to be seen in such states of the atmosphere. 
In the apparatus experimented with at the South Foreland by the 
Trinity House, the condensing principle was also applied, but to a 
very small extent, viz., the condensation of 30° into 5° or 6 times, 
while in the Isle of May apparatus the light proceeding from 45° 
is condensed into 3° or 15 times, and the emergent beam admits of 
being dipped to any extent which may be found necessary during fogs. 
The peculiar property of this azimuthal condensing arrangement 
is that, where the light is intermittent, the power is increased in 
proportion to the intervening periods of darkness. Thus, neglecting 
the loss of light by absorption &c., the power is doubled when the 
periods of light and darkness are equal, trebled when the dark 
periods are made twice as long as the light, and so on in proportion, 
while in every case the rays are spread uniformly over each illu- 
minated sector. 
2. Glories, Halos, and Coronse seen from Ben Nevis Obser- 
vatory. Extracts from Log Book. By B. T. Omond. 
Communicated by Professor Tait. (Plate XYI.) 
Dec. 1, 1883. — Glory seen at 9 h 15 m (see fig. 1). Bed outside 
in both rings. Smaller one almost filled up by shadow of head. 
Badius of outer red = 2°. At ll h 12 m and 12 h 0 m white fog bow. 
When very bright it was coloured red outside. Too large to measure. 
Dec. 6, 1883. — Corona round moon all evening. Bed outside. 
Bluish Badius of red, 2° 8'. Occasionally an outer circle of a 
outside in both. At 22 h corona again. Triple ring, red outside in 
all three. Badius of middle red =1° 45'. At same time lunar 
Bed 
Yellow 
Blue 
bluish colour, extending from red ring outwards to a 
radius of 4°, was visible. 
Dec. 17, 1883. — Corona at 2 h . Double ring, red 
