(415 ) 



XXIV.- — Micrometrical Measures of Gaseous Spectra under High Dispersion. 

 By C. Piazzi Smyth, F.R.S.E., and Astronomer-Royal for Scotland. 

 (Plates XLVIII. to LXXVIII.) 



(Read 16th June 1884.) 



CONTENTS. page 



Introduction, ............ 416 



Part I. — The first Gas to be examined, and under what conditions ? ..... 418 



The Candle-Spectrum, or CH gas in Blow-pipe Flame, ..... 419 



The Spectrum plates employed here, ........ 420 



Principles of Spectrum representation, . . . . .. . . 421 



Maps of the CH Spectrum in Flame, ........ 422 



Advantages of Electric-lighted Gas- Vacuum Tubes, ...... 424 



A London objection to my testimony therein, ...... 425 



Part II. — Citron and Green bands of CH in Vacuum Tubes, ...... 427 



Orange band of CH and effects of Pressure, ....... 428 



Blue and Violet bands of CH, 431 



Marsh Violet band of CH, 432 



Chemical Interpretation of the CH Spectrum, ....... 432 



Part III.— The CO Spectrum, ..;........ 435 



Statical differences, .......... 435 



Green band of CO, .......... 436 



Its numerical explication, ........... 438 



Remaining bands of CO, .......... 439 



Part IV. — Elementary Gases, Subject 1, or H, . . . . . . . . 440 



Elementary Gases, Subject 2, or 0, . . . . . . . . 444 



Elementary Gases, Subject 3, or N, . . . . . . . 446 



Part V. — Concluding Notes on H, 0, and N, , . . . . . .. 450 



APPENDICES. 



Appendix I. Professor Alexander S. Herschel's letter on the Green Band of CO and its 



explications (eventually condensed into Plate 31), ...... 454 



Appendix II. Professor Alexander S. Herschel's letter, on a theoretical point in Plate 31, . 457 



Appendix III. Mr Charles F. Casella's letters on the Preparation and Purification of some of 



his Vacuum Tubes, .......... 458 



Appendix IV. Plates 1 to 31, as follows: — 



PLATES. 



XLVIII. 1 CH in Blow-pipe Flame, Orange band thereof, and Citron band, adapted to a 40-foot 



Spectrum length. 

 XLIX. 2 ii ii Citron band continued and Green band. 



L. 3 ii n Green band continued and Blue band. 



LI. 4 ii ii Violet band thereof. 



LII. 5 I Successive methods of Incandescence tested by the D 1 and D 2 Sodium lines, on an 

 enlarged scale. 

 LIII. 6 CH in Vacuum tubes, Citron band thereof, and Green band, adapted to a 40-foot Spec- 

 trum length. 

 LIV. 7 ii ii Green band continued, Blue band, Violet band, and Marsh Violet 



band. 



VOL. XXXII. PART HI. 



3 Y 



