The Astrophysical journal . splacement of the spectralimage on the film of mm corresponds to a rotation of the gradu-ated circle of 60. MEASUREMENT OF A SECTION I I 2 3 4 5. Distance of Mark at Right Edge from Center of Line in mm GreatestDifference a b a b a b c mm 2o?93 I23 4 6-544 4926-578 228 5 266 B 00 6 260 vOCO 2o?95 7 6-338 34° 6-339 t~~ H I5-I 8 8 260 n II 9 290 0 28 fc> 10 3°9 II 11 6-353 361 6-357 vo °< 12 350 6-356 1 vO 13 6-354 358 6-356 IN O 14 26
The Astrophysical journal . splacement of the spectralimage on the film of mm corresponds to a rotation of the gradu-ated circle of 60. MEASUREMENT OF A SECTION I I 2 3 4 5. Distance of Mark at Right Edge from Center of Line in mm GreatestDifference a b a b a b c mm 2o?93 I23 4 6-544 4926-578 228 5 266 B 00 6 260 vOCO 2o?95 7 6-338 34° 6-339 t~~ H I5-I 8 8 260 n II 9 290 0 28 fc> 10 3°9 II 11 6-353 361 6-357 vo °< 12 350 6-356 1 vO 13 6-354 358 6-356 IN O 14 268 15 217 16i7 218 248 ERNST GIESING The following six curves exhibit the variation of the ruling-spactfor all the six sections of the experiment. The fourth curve fromthe top in Fig. 4 corresponds to section IV, the measurements ofwhich are given in full. The straight line corresponds in all cases tothe diffraction pattern of the full surface of the grating. The accuracy. Fig. 4 of measurements is seen to be not very great on account of the indis-tinctness of the spectral line; the error can amount to a few hundredthsof a millimeter, equal to about 4, but in general would hardly exceed2. The previous experiment shows that by the isolation of a smallnumber of rulings we have to do with very considerable variations; ABSOLUTE WAVE-LENGTH FROM GRATINGS 249 that is to say, we cannot properly speak oj a constant 0} the largest difference between mark and spectral line in the wholeexperiment is Fig. 4, fourth curve; 2 —first curve; 14 = 33*5 = (1 : 3000) difference of the space between rulings. It is a strik-ing fact that sections I and II lie throughout below the line of theimage of the whole grating, whence it would follow that at this edgeof grating Gx the constant was too great throughout. The laterexperiments with wider slit confirmed this fact. In fact, Bell foundsomething similar in his calibrations. Ac
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
