( 729 ) 



Argument , Coefficients in (hi 



Sat I Sat. II Sat. Ill Sat IV 



M + 0.0006 — 0.0102 — 0.0135 — 0?0320 



W - 0.0008 — 0.0012 — 0.0029 



W^ — 0.0001 — 0.0001 — 0.0003 



r, 4- 0.0099 + 0.0028 4- 0.0001 



r, + 0.0016 + 0.0024 — 0.0018 



r^ — 0.0001 -f 0.0019 + 0.0029 -1- 0.0010 



r^—r^ —0.0027 —0.0011 —0.000.5 

 r^—r, —0.0005 — 0.0002 — 0.0001 

 r^—r, +0.0011 —0.0005 —0.0013 —0.0010 



t5,-w, —0.0005 -f 0.0002 +0.0009 —0.0011 



It should be kept in mind tliat all the above developments are 

 based on Soun.i, art's analytical theory. New values of the masses and 

 elements were introduced into his formulas, and a few numerical 

 mistakes were corrected, but the analytical formulas were not altered. 

 The only exception is the expression for the period of the libration, 

 which \vas computed to terms of the third order in the masses 

 inclusive, while Souili.art rested content wilh those of the second 

 order (See Gron. Publ. 17, art. 18). 



Physics. — ''An auto-coUimating spectral apparatus of great 

 hcDiinous tntensitif' , by Prof. H. E. J. G. du Bois, G. J. 

 Elias and F. Lowe. (Communication from the Bosscha-Labo- 

 ratory). 



In optical work an illuminator is often wanted, which combines 

 great brightness with monochromatic purity of the light, if possible 

 of the order 0,1 {^if^i. In spite of the almost boundless variety of 

 available spectral apparatus ^), such an appliance is wauting. For this 

 purpose WiiLFiNG -) it is true, constructed a monochromatoi' and 

 investigated the luminosities obtainable by means of different sources 

 of light, but its aperture was only \/g, the dispersion also rather 

 slight. An auto-collimator lately described by Fahry and Jobin ^) has 

 an aperture of only 7^,,. Recently one of us has described three 

 spectral a|)paratus with constant deviation (parallel or at right ano-le) ^); 



1) H. Kayser, Handb. d. Spectroscopie 1, p.p. 489 et seq. gives a survey leading 

 up to 1900. 



2) E. A. WüLFiNG, N. Jahrb. f. Mineralogie Beil. 12, p. 343, 1898. — C. Leiss, 

 Zeitschr. fiir Instr. kunde 13 p. 209, 1898. S. Nakamura, Ann. d. Phys. (4) 20 p. 

 811, 190G. 



■5) Ch. [''abry t'C' A. JoBiN, Journ. de Phys. (4) 3 p. 202, 1904. 



*) F. Lowe, Zeilschr. f. instr. Kunde 26, p. 330, 1906 and 27, p. 271, 1907. 



