28 H. A. LENEHAN. 
copes of 5 and 63 inch aperture clamped to the same 
frame—work. As for the work planned with this 
instrument it is necessary to make long uninterrupted 
exposures; the mounting has been so designed as to give 
a continuous motion across the meridian without reversal 
of the telescope. The focal length of the 10 inch lens is 
only 50 inches (128cm.) so that it is exceedingly rapid; it 
gives exquisite definition over a field about 7 in width, 
and by careful averaging may be made to cover a region 
of 9°. The plates used are 12 inches square, and the scale 
of photograph such that lin = 1°14° or 1°. = 0°88 inch. 
Guiding is performed with a high power eye piece on a 
o-inch telescope. For use in southern latitudes reversal 
gearing is provided in the driving train from the clock. 
The instrument was taken in Decemher, 1904, to Mount 
Wilson, in Southern California, where there is being 
established a branch Observatory of the Yerkes Institution. 
It is intended to replace the 6; lens by a new one of Jena 
glass, and an objective prism of the same aperture for 
spectroscopic investigation. 
The Mount Wilson Observatory.— HE. \W. Maunder, 
F.R.A.S., gives the following description of the Observatory 
on Mount Wilson, California, U.S.A. :— 
A most important step for the advancement of astronomy has 
been taken by the establishment of a Solar Observatory on 
Mount Wilson in Southern California, at an elevation of about 
6000 feet, in an atmosphere free, through exceptionally long 
periods, from cloud, water vapor, dust, fog, or wind; its position 
is in latitude 34° 13’ 46” north and longitude 118° 3’ 40”, and is 
not far distant from the cities of Pasadena and Los Angeles. 
The plan of work proposed includes the following classes of 
observation :—(1) Frequent measures of the heat radiation of the 
sun, to determine whether there may be changes during the sun 
spot cycle in the amount of heat received from the sun by the 
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