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CARNEGIE INSTITUTION OF WASHINGTON. 



investigation had revealed errors in the Rowland wave-lengths 

 comparable in sign and magnitude to the deviations observed by 

 Albrecht, the 104 hnes used by him were investigated. The cor- 

 respondence between the Albrecht deviations and the results of this 

 investigation affords so close a parallel as to leave no doubt that the 

 deviations are to be attributed to systematic errors in Rowland's 

 tables. They furnish no valid evidence, therefore, that the relative 

 positions of the Fraunhofer lines are systematically displaced by mutual 

 influence, while, as just shown, the sun-arc displacements (372 Unes) 

 and the relative separations of the components of 45 close pairs in 

 solar and arc spectra indicate that, within the limits of error, mutual 

 mfiuence is absent from the solar spectrum. In so far as mutual 

 influence is a necessary corollary of anomalous dispersion, evidence for 

 the latter is therefore also absent. 



INVESTIGATIONS OF PLANETS, STARS. AND NEBUL/E. 

 OBSERVING CONDITIONS. 



The obsei*ving conditions at night for the year ending August 31, 

 1916, were more favorable than for several years past. This was in 

 spite of the fact that January was one of the stormiest months on 

 record and furnished the lowest percentage of observing weather 

 (14 per cent) since the establishment of the Observatory. The 

 months of April, May, and June were exceptionally favorable for 

 observational work, summer conditions beginning much earlier than 

 usual. The 60-inch reflector was in use 210 entire nights and during a 

 part of 78 nights. No observations were made on 78 nights. Out of 

 3,591 hours of darkness the instiniment was in use 2,306 hours, or 64 

 per cent. The mirror was resilvered twice during the year, in February 

 and June. The statistics for each month are given below : 



