NO. 17 SMITHSONIAN EXPLORATIONS, IQI6 133 
As the sun is the ruler of the earth’s temperature, and his rays 
the dependence of all vegetation, solar fluctuations of five, or even 
sometimes ten per cent, such as have been discovered in these studies 
must be important. Great need is apparent of checking and com- 
pleting the Mount Wilson work at other favorable stations. In 
1914 Mr. Abbot went to Australia and urged the erection of an 
observatory for the purpose there, but owing to the outbreak of the 
war, the Government, though favorably inclined, was unable to take 
the matter up. Fortunately it has recently become possible for the 
Smithsonian Institution itself to undertake the support of a station 
in South America for observing solar radiation, and this is expected 
to be installed in July, 1917 by Mr. Abbot. It is hoped to make the 
solar radiation observations every day in the year hereafter either 
at Mount Wilson or in South America or at both stations. 
Further work was done with a solar cooking appliance at Mount 
Wilson in 1916, but owing to the delay until September of materials 
ordered for it and expected in April, no satisfactory tests have yet 
been made. [ood was cooked in 1915, including meat, potatoes and 
other vegetables, and cereals. It is confidently expected to bake bread 
also when the apparatus is done. 
A great drawback to the solar work done hitherto has lain in the 
tarnishing of the silvered mirror surfaces used to reflect the sun rays 
onto the bolometer. This is the more serious because it affects rays 
of different colors differently. Violet and ultra-violet rays are most 
weakened by the tarnishing of silver. At last a new alloy “ stellite ” 
has appeared which does not tarnish, even if exposed for months to 
sun, rain, snow, and smoke. ‘Two stellite mirrors for the spectro- 
bolometer were introduced on Mount Wilson in 1916, along with a 
vacuum bolometer of greatly increased sensitiveness. It is now 
hoped to determine definitely whether all rays of the sun wax and 
wane in their intensity proportionally, as the sun varies, or increased 
solar radiation 1s preponderatingly associated with special regions of 
the spectrum. 
Comparisons were made in 1916, of the pyrheliometers used daily 
in Mount Wilson work with the standard waterflow pyrheliometer. 
The results showed that no detectable change of the sensitiveness 
of the secondary pyrheliometers has occurred. We may be confi- 
dent that the entire series of observations at Mount Wilson, from 
1905 to 1916, 1s expressed on a constant scale of radiation to within 
one per cent. Numerous and varied measurements show also that 
this constant scale is the true standard scale of measurement whose 
