---------------------+----+---------+------+-----+-----------+----------- Observers. |Red.| Yellow. |Green.|Blue.| Indigo. | Violet. ---------------------+----+----+----+------+-----+-----+-----+------+---- | | | | | | | |{4694}| Vogel, April 9, 1871 |6297|5569|5390| 5233 | 5189| 5004| — |{ to }| — | | | | | | | |{4629}| | | | | | | | | | Barker, Nov. 9, 1871 |6230|5620| — | — | 5170| 5020| 4820| — | — | | | | | | | | | | | | |{5330}| |{5050| 4930| 4740}| Barker, Oct. 14, 1873|6300|5550| — |{ to }| — |{ to | to | to }|4310 | | | |{5200}| |{4990| 4850| 4670}| A. Clarke, junr., | | | | | | | | | Oct. 24, 1870 | |5690| — | 5320 | — | — | 4850| — |4350 | | | | | | | | | Backhouse, 1873 |6060|5660| — | — | 5165| 5015| — | 4625 |4305 | | | | | | | | | Backhouse, Feb. 4, | | | | | | | | | 1874 | * |5570| — | — | 5180| 4980| 4830| 4640 |4320 | | | | | | | | | H. R. Procter, 1870 | * | * | — | * | — | — | — | * | * | | | | | | | | | Lord Lindsay, 1870 | — | * | * | * | * | — | — | — | * ---------------------+----+----+----+------+-----+-----+-----+------+---- * Mr. Procter’s and Lord Lindsay’s lines had no wave-lengths. [Sidenote: Ångström’s drawing discussed.] On examining Ångström’s diagram it certainly seems to me that, upon the showing of the drawing itself, the coincidences are not very exact. All three of the violet-pole bands appear to be less refrangible than the Aurora-lines with which they are compared-the middle one (at 47) considerably so, the one near E (at about 52·30) appreciably so, and the third (at 43) slightly so. [Sidenote: Diagram of Vogel’s Aurora and violet-pole spectrum.] As it seemed desirable to adopt a specific Aurora-spectrum for comparison, and to show such comparison on a somewhat larger scale than Ångström’s drawing, I prepared the diagram shown on Plate XI. fig. 1. The upper spectrum is Vogel’s, already described and figured on Plate XIII. The lower spectrum is that of “Air, violet pole,” Plate XV. spectrum 2, graphically shown. I can only find one absolute coincidence in the two compared spectra in this diagram.