28 



SCIENCE 



[N. S. Vol. XXXVII. No. 940 



sion was found, consisting of tlie zonal harmonics 

 of the first and third order, which represents the 

 facts to within one per cent. 



Supposing the bound electrical charges in each 

 atom of the earth to be separated by some cause 

 into positive and negative atomic charges an infin- 

 itesimal distance apart, such that the total charge 

 throughout the earth of each kind of electricity be 

 equal and the volume density of each charge vary 

 from parallel to parallel as sin" u; then, by 

 reason of the earth's rotation, a magnetic field 

 results whose potential is the expression mentioned 

 in the preceding paragraph. The first term corre- 

 sponds to a uniform magnetization of the earth 

 parallel to its axis of rotation having about one 

 tenth of the strength of the total portion assign- 

 able to a imiform field; the second term, consist- 

 ing of the third order harmonic, reproduces satis- 

 factorily the observed increase in the character- 

 istic functions. If it be assumed that the sepa- 

 rating agency is the component of the earth's 

 centrifugal force acting in the direction of the 

 radius away from the center, a distribution of 

 the two opposite electricities throughout the earth 

 would apparently result, following, as a first ap- 

 proximation, the same law of density, supposed in 

 deriving the expression, the zonal harmonics. 

 Before a final statement, however, can be made 

 as to the precise cause, a more complete examina- 

 tion will have to be made and full consideration 

 be given to all the various effects involved. 

 Badial Motion in Sun-spots: C. E. St. John. 



The results obtained to date indicate the fol- 

 lowing mean conditions: 



Results similar to those of iron appear for other 

 metallic vapors producing lines of moderate in- 

 tensities, though the velocities from lines of equal 

 intensities for different elements are not equal. 



This offers a means of determining the relative 

 levels at which lines of different intensities have 

 their origin, in terms of some standard such as 

 iron. 



Three regions are indicated in the solar atmos- 

 phere surrounding spots with the following char- 

 acteristics at the different levels: (1) The upper 

 chromosphere, motion inward, shown by the H 

 and K lines of calcium and H of hydrogen; 

 (2) an intermediate region shown by the D lines 

 of sodium, b lines of magnesium, and the strong 

 aluminum and iron lines, motion inward generally 

 prevailing; (3) a lower region of outward motion, 

 velocity increasing with lower levels, on the as- 

 sumption that when considered by and large the 

 weaker lines are associated with the lower levels. 

 Pressure in the Solar Atmosphere : C. E. St. John. 

 In the new spectrograph of the 150 -foot tower 

 telescope the sources of error associated with the 

 instability of the apparatus, the Olumination of 

 the grating and the centering of the solar image, 

 have been overcome, the first, by the massive con- 

 struction of the spectrograph, the head of which 

 weighs about 4,500 lbs.; the second, by the larger 

 diameter, 15 inches, of the cone of sunlight inci- 

 dent upon the grating which the long focus, 75 

 feet, of the spectrograph permits when the 12-inch 

 objective of 60-feet focus is used to form the 

 solar image on the ^lit; the third, by fixing the 

 slit rigorously on the axis of the centering circles. 

 The error introduced from non-centering of the 

 image may be large; with the image now used 

 (diameter 162 mm.) the solar lines would be 

 shifted 0.001 A. by solar rotation when the slit 

 is 2 mm. from the center of the image and on 

 small images the error might be much greater. 



With this equipment an investigation involving 

 a comparison of the arc and solar spectra of iron 

 is being carried out. The preliminary results show 

 that the solar lines of iron classified in accordance 

 with their displacement in solar spectrum fall into 

 the classes suggested by Gale and Adams in their 

 study of pressure shift under laboratory condi- 

 tions and indicate pressures in the solar atmos- 

 phere varying from 0.7 to 6.5 terrestrial atmos- 

 pheres for the different groups. 

 On the Diurnal Variations of Atmospheric Pres- 

 sure: W. J. Humphreys. 



It has been known for nearly two and a half 

 centuries that there are more or less regular daily 

 variations in the height of the barometer, cul- 

 minating in two maxima and two minima during 

 the course of the 24 hours; the maxima occurring 



