MOUNT WILSON SOLAR OBSERVATORY. 239 



The Stark effect is nevertheless of such fundamental importance 

 that it has seemed advisable to study it carefully in our laboratory. 

 We owe to Professor Stark's kindness a beautifully made hydrogen 

 tube of the form he has used so successfully. In the absence of a 

 skilled glass-blower, however, it has been necessary usually to employ 

 the simple fonn of tube used by Lo Surdo. Miss Howell, after success- 

 fully overcoming the difficulties encountered in the course of this work, 

 has obtained some interesting new results for lines of lithium and cal- 

 cium. For the Uthium lines X4602 and X4132 she finds in the trans- 

 verse effect the same general character of separation as that described 

 by Stark, though her measurements give, on the whole, larger displace- 

 ments than he found. In the longitudinal effect, however. Miss 

 Howell's photographs show two sets of unpolarized components which 

 correspond in number, and roughly in intensity, with those observed 

 in the transverse effect, but which have distinctly smaller displace- 

 ments. In addition, the strong central component of X4132, moder- 

 ately shifted toward the violet, is found unpolarized in both the 

 longitudinal and transverse effects. Displacements toward the violet 

 are greater than those of opposite sign, reaching a maximum of 3.1 A for 

 20,000 volts per centimeter in the case of the transverse effect for X4132. 



The H and K lines of calcium are each resolved by an electric field 

 into two components for the transverse effect and three for the longi- 

 tudinal. In the latter case all these components are unpolarized and 

 are sharp and clear. For the transverse effect, however, the com- 

 ponents are broad and hazy, the stronger one, on the red side, being 

 unpolarized in each case, while the weaker one is polarized. The 

 maximum displacement occurs in the case of the K hne, amounting to 

 about 1.4 a toward the red for 20,000 volts per centimeter in the 

 longitudinal effect. This is comparable to the separations observed 

 in the case of hydrogen, helium, and lithium. 



The lithium line here in question does not exist in the sun, and it 

 jemains to be considered whether the wings of the H and K lines in 

 spot spectra are due to an electric field. When we remark the great 

 strength and breadth of these wings outside of spots, and remember 

 how easily similar v/ings are produced in the laboratory without the 

 aid of an electric field, it can not be said that such indications are yet 

 entitled to any weight. Steps are now being taken to produce more 

 brilliant spectra, since high dispersion must be employed to determine 

 whether Hues of iron and other similar elements are appreciably 

 affected by an electric field. 



GENERAL MAGNETIC FIELD OF THE SUN. 



The chief work of the year has been a continuation of the attempt to 

 determine the incUnation of the sun's magnetic axis and the period of 

 its revolution about the sun's axis of rotation. The three lines 

 X 5247.737, X 5300.929, and X 5329.329 have been measured by Mr. 



