990 Marvels of the Universe 
twenty-two between midnight and eleven a.m. Thunderstorms are of daily, almost hourly, 
occurrence in the Tropics on a scale which we in more temperate zones can scarce form any 
conception of. 
Yet for all their frequency, our knowledge as to the development of electricity in these 
outbursts is by no means satisfactory; though from time to time more or less plausible 
hypotheses have been put forth, the subject is still a mysterious one, and we must be 
content to wait for further light. Dr. Simpson, of the Indian Meteorological Department, has 
outlined one theory. He supposes that upward currents of air prevent rain that would other- 
wise be deposited from falling. The raindrops increase in size “‘ through cycles of growth,” 
then break up with separation of electricity, until their charge is so great as to produce a 
gradient of more than thirty thousand volts per centimetre. Then the lghtning flashes, the 
thunder rolls and the accumulation is neutralized over a limited area; this process continues, 
another flash, and then another, and so on till equilibrium is attained and the storm ceases. 
THE HORNED CURASSOW 
BY SIR HARRY JOHNSTON, G.C.M.G. 
THE Curassows and Guans belong to a family (entirely restricted in its distribution to Central and 
South America) of the same order as 
the Pheasants and the Australian 
Mound-builders. Some of the Curas- 
sows, indeed, will hybridize with 
certain old-world pheasants; but, of 
course, the forms derived from this 
cross are infertile mules. The differ- 
ences between pheasants and turkeys, 
on the one hand, and Curassows, on 
the other, lie chiefly in the position 
of the hind-toe and other structural 
points, and in the life-habits, which in 
the Curassows are arboreal. These 
handsome South American _ birds 
usually (but not always) build their 
nests in trees. 
Of the three sub-families of Curas- 
sows, the one which most nearly 
approaches the turkeys, pheasants and 
guinea-fowl in affinities is the rare 
and beautiful Lord Derby’s Mountain 
Pheasant of Guatemala, which I have 
illustrated in colour from two re- 
markably fine specimens—male and 
female—to be seen in the Museum of 
Natural History at Leiden, Holland. 
Probably no living specimen of this 
ASD ED [Harvard Observatory. species has ever been exhibited in the 
LIGHTNING. : F = 
London Zoological Gardens, though 
This photograph shows the spectrum of a lightning flash, by which : : 
it seems that the celebrated Lord 
means the electric light is broken ‘up into its component colours as in- 
dicated by the lines of differing intensities. Derby of the middle of the nineteenth 
