TRANSACTIOXS OF SECTION A. 5u5 



6. Spectrograms of Jujnler, Uranus, and Vesta. By Peucival Lowell. 



Both I. and II. (spectrograms of Jupiter) were taken, practically at tlie same 

 epoch, about two months before opposition, 1902. The bpectrum of the planet 

 occupies the centre, the comparison spectrum, iron, lying on both sides. 



I. Slit i)arallel to the polar axis of tlie planet. The dark lines of tlie planet's 

 spectrum run straight across, but are all shifted noticeably toward the viok't, 

 due to the earth's approaching Jupiter at the time. By measuring this shift it is 

 possible to tell the date of the photograph. 



Running lengthwise of the spectrum, and on either side its centre, are two 

 hazy dark bands. These are the dark tropical belts of the planet. This is proved 

 by com])arison with II. in which they are absent. 



II. 81it parallel to planet's equator. No lengthwise dark bands visible, the 

 slit taking in only the light equatorial region between them. 



The lines in this photograph all slant from the lower right-hand side to the 

 upper left-hand side when the violet end is made the top. This is the effect of the 

 planet's rotation and is very evident. 



Furthermore, the right side of the planet's spectrum fades off, the left side 

 ending abruptly. This is due to the planet's phase. It lieiug before opposition, 

 tlie phase was on the side carried away from the earth by the body's rotation. 

 This agrees with the shift in the lines— toward the red on the right. In I., on 

 the other hand, both sides of the spectrum band are nearly alike and both ari; 

 more definite than the right side of 11., less so than the left side of it. This 

 agrees with the known fading out of the planet toward the limb — when full. 



III. Spectrogram of Uranus with Saturn for comparison spectrum on either 

 side. 



A dark band appears in the spectrum of Uranus in the yellow, which has no 

 counterpart in that of Saturn. 



IV. Spectrogram of Vesta with Saturn as comparison spectrum on either hand. 

 Vesta's spectrum has no gaps like that of Uranus. 



7. The Uncertainty of our present Knowhdqe of the Distance of the Sun, 



By A. K. HiNKs. 



In 1896 it was resolved to adopt in all the Nautical Almanacs a uniform value 

 8"-80 for the solar parallax. The four determinations of principal weight 

 were : — 



From Gill's lieliometer observations of minor planets, 8"'802. 



From all determinations of the constant of aberration, 8"'799. 



From all determinations of the parallactic inequality of the Moon, 8"'79-ii 



From mass of Earth found from motion of node of Venus, 8''''7G2. 



The evidence was thus three to one in favour of 8"'80. 



Since this discussion was completed by Newcomb, the evidence has begUn to 

 give way. New determinations of the aberration constant and of the theoretical 

 relation between the parallactic inequality and the solar parallax have agreed in 

 reducing two of the results, so that the evidence now stands — 



From Gill's heliometer observations of minor planets, 8"'802. 



From constant of aberration of light (Newcomb's latest discussion), S"'777. 



From the parallactic inequality of the moon, less than 8""773. 



From motion of node of Venus, 8"'762. 



The evidence is now three to one in favour of a Aalue less than 8"'78. It 

 is therefore peculiar!}- important to know as soon as possible the result of the 

 observation recently made upon Eros. The author outlined a scheme by which 

 nine days' photographs made and measured at some eight observatories would be 



