166 



SCIENCE 



[N. S. Vol. XXVII. No. 683 



Miller upon the fact that dividing by 

 should be banished from elementary mathe- 

 matics. The so-called indeterminate forms 

 are really meaningless forms and it is ques- 

 tionable whether one should speak of 

 evaluating such a form. As uv = has 

 not always for its locus the combined loci 

 of w = and v = the rule relating to 

 this case should be stated with the neces- 

 sary restrictions. The fact that the last 

 letters of the alphabet are used both for 

 variables and for unknowns in elementary 

 algebra has led some authors to speak of 

 these two very distinct concepts as if they 

 were identical. This is the more unfortu- 

 nate since the concept of a variable is con- 

 tinually playing a more fundamental role 

 in elementary algebra. This paper will 

 appear in School Science and Mathematics. 



20. Photographic and visual magnitudes 

 are determined in immediate succession 

 with the 24-inch reflecting telescope; the 

 photographic on ordinary plates, the visual 

 on orthochromatic plates used with a suit- 

 able color-filter. The spectral types are 

 obtained with an objective prism used on 

 a 6-inch Zeiss doublet. The difference be- 

 tween the photographic and visual magni- 

 tudes, zero for white stars, increases pro- 

 gressively with the intensity of color and 

 with the change in spectral type, giving a 

 measure of color. 



The distinctive features of the present 

 work are: (1) The substitution of measures 

 for eye-estimates of star-color, (2) the com- 

 parison of measured colors with spectral 

 types. . 



Star colors ranging from i to 5 or more 

 magnitudes are found for types i^ to iV in 

 the Harvard classification. It is proposed 

 to use these color- values as an improved 

 method of stating star-colors. The paper 

 will appear in the Astrophysical Journal. 



21. In this paper Mr. Fox presents the 

 evidences proving the identity of certain 

 features seen on the calcium spectro- 



heliograms and the eruptive prominences. 



22. The objective was tested for zonal 

 and astigmatic errors by Hartmann's 

 method. The astigmatic errors are negli- 

 gibly small. Hartmann has introduced a 

 criterion for comparing various objectives, 

 Avhieh is the mean diameter of the star 

 image from the various investigated zones 

 of the objective upon the mean focal plane 

 expressed in 1/100,000 of the focal length. 

 Data were given for the 40-inch objective 

 of Yerkes Observatory and diagrams were 

 exhibited. This paper will appear in the 

 Astrophysical Journal. 



23. Mr. Wallace considered the following 

 points: Importance of the method to as- 

 tronomers in general. Factors governing 

 successful photographic results and the 

 role of personality. The requirements and 

 adjustment of filter and plate to the visual 

 refracting telescope, illustrated by color 

 curves of filters, plates and objective, and 

 their combined effect upon the images ob- 

 tained. Halation, and its influence upon 

 the recording of faint or delicate details. 



24. The paper describes a vertical 

 coelostat telescope recently erected on 

 Mount Wilson. A 12-inch objective, 

 mounted at the summit of a steel tower 

 65 feet in height, receives the sun's rays 

 from a coelostat and second mirror and 

 forms an image in a house at the base of 

 the tower. Professor Hale stated that the 

 principal advantages of this instrument, 

 as compared with the Snow telescope, are 

 the better definition of the solar image and 

 the much smaller change of focus during a 

 given exposure of the mirrors to the sun. 

 Photographs of the spectra of sun-spots 

 made in the fourth order of a Littrow 

 spectrograph of 30 feet focal length, 

 mounted in a pit, excavated in the earth 

 underneath the tower, were projected on 

 the screen. 



25. Solar spectra, corresponding to 



