154 SOLAK ECLIPSE OF MAY 28, 1900. 



intentionull}" over-exposed, in order to better exhibit tlie romarkal)le 

 polar streamers, extending here to a distance of about six minutes 

 from the sun, but still further in Mr. Child's telescopic drawing (not 

 given). 



Plate IV is a view of a small part of the apparatus on the field, 

 including the terminus of the 135-foot horizontal tube with its canvas 

 covering, which has been described as like an extended A tent. The 

 photographic room is seen at the end of the tube and beyond that the 

 tube containing the lens loaned by Professor Young, pointing directly 

 skyward. In the immediate foreground is the 5-inch equatorial. 



That it will be impracticable to give here all of the disk of the moon 

 in the large photographs will be evident when it is considered that the 

 lunar circumference on each plate is about tt feet; but it will be inferred 

 from the examples that the prominences and polar streamers, as well 

 as their features, appear in imposing magnitude and detail. 



Many of what it is hoped will be. most interesting photographs still 

 await development, but Mr. Smillie's thorough preparation is promis- 

 ing adequate results. 



HEAT OF CORONA. 



Mr. Abbot, with the aid of Mr. Mendenhall, appears to have meas- 

 ured the heat of the corona, and in spite of previous efiorts this is 

 probably the first time that it has been really shown to exist. For 

 five minutes before second contact the bolometer was successfully 

 exposed to the region of the sky close to the narrowing crescent of the 

 sun where the corona was shortly to appear. A diaphragm was inter- 

 posed in the beam having an aperture of onl}" O.-l square centimeter, 

 and deflections rapidly diminishing from 80 to 6 millimeters were 

 obtained, the last being about fort}" seconds before totalit3^ Then the 

 diaphragm was opened to 290 square centimeters and a negative deflec- 

 tion of 13 millimeters was observed after totality, where these positive 

 deflections had just been found, showing that the corona was actually 

 cooler than the background which had been used at the room tempera- 

 ture. Next the black surface of the moon was allowed to radiate upon 

 the bolometer, and the still larger negative deflection of 18 millimeters 

 was observed.^ 



^ Additional note, April, 1901.— It will be observed that three fundamental observa- 

 tions were taken, (1) on a screen of dark cardboard of the temperature of the bolom- 

 eter ; (2) on the dark body of the moon, and (3) on the inner corona. There was 

 unfortunately not tin:ie to take a fourth on the sky near the corona, which was desir- 

 able though not indispensable. 



These three observations give the following readings: The one on the screen was 

 arbitrary, and calling it zero, that on the dark moon was minus 18, and that on the 

 inner corona was minus 13. The sky radiation during the last two in neighboring 

 regions is taken as equal. The algebraically increased reading for the coronal radia- 

 tion, then, was probably due to this radiation being superposed on that of the sky. 



Since the eclipse the bolometer has been set ou a screen of its own temperature, 



