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ASTRONOMY- R. W. WOOD 
the same as with the silver film, while the time of exposure is only about 
one-tenth as long. 
In October, through the courtesy of Dr. G. E. Hale, Director of the 
Mt. Wilson Observatory, the 60 inch reflector was placed at my dis- 
posal for four nights, and by working continuously from sunset to dawn, 
I was able to secure a very complete set of pictures of the moon in yel- 
low and ultra-violet light and some forty negatives of Jupiter and Saturn 
in infra-red, yellow, violet and ultra-violet light. The telescope was 
used at the eighty foot focus and as the mirrors were silvered, the 
region of the spectrum utilized for the ultra-violet photography was 
slightly less refrangible than in the earher work. Preliminary experi- 
ments had been made on the spectrum of sunlight after three reflections 
from silver and transmission through the bromine cell. Full data re- 
garding these matters will be published shortly in the Astrophysical 
Journal. 
Extremely interesting results were obtained in the case of Saturn. 
The infra-red picture, taken by wave lengths above 7200, showed the 
ball of the planet almost devoid of surface markings, the merest trace 
of the faint narrow belts appearing. The photographs made with the 
yellow screen showed the belts distinctly, giving about the same im- 
pression as visual observations. On the plates made with the violet 
ray-filter (transmission 4000-4500), a very broad dark belt surrounded 
the planet's equator, occupying the region of the planet which was 
brightest in yellow light. In addition to this dark equatorial belt a 
dark polar cap of considerable size appeared in the pictures. So dif- 
ferent were the two pictures that, were it not for the ring, it would be 
difficult to beheve that they represented the same object. In ultra- 
violet light the appearance was much the same, but the dark belt was 
not quite so wide, the bright region between the polar cap and the belt 
being distinctly broader. 
Photographs made with the four monochromatic filters are reproduced. 
Two hypotheses suggested themselves in explanation of the dark belt, 
We may be dealing with a fine mist or dust which forms an extension of 
the crepe ring down to the ball of the planet. This hypothesis appears 
to be favored by the circumstance that on the negatives made by ultra- 
violet light (and to a less degree by violet) the sky between the ball of 
the planet and the ring is distinctly denser than the region just outside. 
This would indicate that the region inside of the ring was filled with some 
material which reflected the short wave-lengths to a slight degree. No 
trace of this darkening appears on any of the plates made with the 
yellow screen, even on one that was many times overexposed, which 
