[160] The figure has to be enormously exaggerated, the angle SσE as shewn there being about 10°, and therefore about 100,000 times too great.
[161] Sir R. S. Ball and the late Professor Pritchard ([§ 279]) have obtained respectively ·47″ and ·43″; the mean of these, ·45″, may be provisionally accepted as not very far from the truth.
[162] An average star of the 14th magnitude is 10,000 times fainter than one of the 4th magnitude, which again is about 150 times less bright than Sirius. See § 316.
[163] Newcomb’s velocity of light and Nyrén’s constant of aberration (20″·4921) give 8″·794; Struve’s constant of aberration (20″·445), Loewy’s (20″·447), and Hall’s (20″·454) each give 8″·81.
[164] Fundamenta Nova Investigationis Orbitae Verae quam Luna perlustrat.
[165] Darlegung der theoretischen Berechnung der in den Mondtafeln angewandten Störungen.
[166] E.g. in Grant’s History of Physical Astronomy, Herschel’s Outlines of Astronomy, Miss Clerke’s History of Astronomy in the Nineteenth Century, and the memoir by Dr. Glaisher prefixed to the first volume of Adams’s Collected Papers.
[167] This had been suggested as a possibility by several earlier writers.
[168] The discovery of a terrestrial substance with this line in its spectrum has been announced while this book has been passing through the press.
[169] Observations made on Mont Blanc under the direction of M. Janssen in 1897 indicate a slightly larger number than Dr. Langley’s.