64 Kansas Academy of Science. 



When the Bunsen line of 160 is examined, the Duboscq number is 

 150. Drawn on the original scale the Duboscq curve is not quite 

 a straight line, but has slight deviations, which are not noticeable 

 when reduced to one-fourth the size, as in the diagram accompany- 

 ing this paper. By the aid of this curve any observed line may at 

 once be compared with the Bunsen charts. In a like manner a 

 curve from KirchhoflP's scale numbers is prepared, only in this case 

 the spectrum lines were obtained from the electric spark. It was by 

 this means that Kirchhoff obtained most of his numbers. His 

 spectroscope contained four prisms of flint glass, three of which 

 had a reflecting angle of 45 degrees and the fourth an angle of 60 

 degrees. These were mounted on metallic stands with leveling 

 screws, and suitably placed on a circular iron plate, upon the rim 

 of which the telescopes were clamped. The light for the metallic 

 spectra was obtained by three or four Bunsen elements acting on a 

 large RuhmkorfP induction coil. A heliostat directed tlie solar 

 rays upon the object-glass of his collimator, and his first care was 

 to represent the lines of the solar spectrum as faithfully as possible, 

 as they appeared in his spectroscope. The distance apart of the 

 lines was measured by movement of an arm which was attached to 

 the observing telescope, and this movement was estimated by the 

 divided circle, with a micrometer screw attached. Record was 

 made of the lines on a chart by means of a kind of equal-part ma- 

 chine, and the intensity and breadth of the lines were shown, the 

 former by three shades of ink. Above the spectrum as thus ex- 

 hibited he placed a millimeter scale, with a starting-point selected 

 at pleasure. He chose such a position as brought the D line very 

 near the 100 mark on the scale. After the solar spectrum was thus 

 recorded, KirchhoflP proceeded to find the places of the metallic 

 spectral lines as compared with the dark solar lines. To accom- 

 plish this he observed simultaneous spectra of the sun and of the 

 metals. The solar beam was received into the upper half of the 

 slit, and the metallic rays into the lower half, first falling on a 

 glass prism so placed over the lower part of the slit that the ray, 

 after a twofold total reflection, fell into the field desired. 



The results of these observations were recorded with the same 

 care as the former, and both were repeated until satisfactory agree- 

 ment was obtained. Kirchhoff observed that a great difference re- 

 sulted in the appearance of the lines as the temperature changed 

 and as other vapors were present. Angstrom denies that there is 

 any real change in the position of the lines, and takes issue with 

 Plucker on this point. Kirchhoff's observations extended from 



