THE MOTION OF ARCTURUS IN THE LINE OF SIGHT.
James Edward Keeler · Publications of the Astronomical Society of the Pacific · 1890
Publications of the same origin.Considering the small differences in the above table to be due to errors of observation, we have 47.96 tenth-metres for the difference of position of the two lines ; hence the wave-length of the second line is for N. G. C. 7027 4958.2 tenth-metres for G. C. 4373-4956.9"or for the mean of the ten nebulas on page 278, 4957.7 tenth-metres.The values obtained by other observers are as follows :Huggins X 4957.0