APPENDIX III. 



ADDITIONAL DATA ON SELECTIVE REFLECTION AS A FUNCTION 

 OF THE ATOMIC WEIGHT OF THE BASE. 



As this work goes to press the experiments of Morse 1 have been pub- 

 lished, and since it contains considerable new data for the region of the 

 spectrum from 10 to 15 fi, it is included here for the sake of completeness. 



In that paper considerable comment is made upon the fact that the 

 writer (see Carnegie Publication No. 65) missed the reflection bands in 

 calcite and in magnesite, previously found by Aschkinass at n to 12//. 

 In reply it may be stated that these two substances were examined in the 

 preliminary work on reflection spectra, in order to get a check on the 

 calibration; and, on finding the reflected energy very weak, no attempt 

 was made to locate the bands known to be at 11 to 12 /<. In this work 

 a Rubens thermopile (heavy wires) was used, which was sluggish and was 

 disturbed by air-currents. Although the sensibility was higher than in 

 the radiometer previously used, the small deflections were not so reliable 

 and no attempt was made to locate weak reflection bands beyond n /, 

 such as are found in the carbonates. This demonstrates the superiority 

 of the radiometer for measuring weak radiation. 



The investigation of weak reflection spectra in the extreme infra-red is 

 accomplished under great difficulties, and Morse has done an excellent 

 service in obtaining data in this region of the spectrum. He used a 35 cm. 

 focal length mirror spectrometer as compared with the writer's 52 cm. 

 focal length mirrors. In the larger spectrometer the energy in the spec- 

 trum is much weaker, while the resolution is greater. The shorter focus 

 does not militate against the results, however, which show that the simple 

 atomic weight relation among the carbonates found by the writer at 6 to 

 8 p. holds for the long wave-lengths at n to 15 fi, where the dispersion is 

 considerably greater. The writer found the reflection band of the carbon- 

 ates at 6 fi very complex (see Chapter III) and it would be interesting 

 to learn whether the bands at 11.4 to 15 fi are likewise. In table X are 

 given the maxima of the reflection bands of the carbonates examined by 

 Morse. It contains one new substance, MnC0 3 , not examined by the 

 writer. The values of the maxima of the first band are not always in 

 agreement, but this appears to be due to the difference in resolving power 

 of the two instruments. In fig. 43 are plotted the wave-lengths of the 



1 L. B. Morse: Astrophys. Jour., 26, p. 225, 1907. 



177 



