416 



C. PIAZZI SMYTH ON MICRO-METRICAL MEASURES OF 



Appendix IV. Plates — continued. 



PLATES. 



LV. 



LVI. 



LVIL 



LVI 1 1. 



LIX. 



LX. 



LXI. 



LXIL 



LXIII. 



LXIV. 



LXV. 



LXV1. 



LXVII. 



LXVIII. 



LXIX. 



LXX. 



LXXI. 



LXXII. 



LXX 1 1 1. 



LXXIV. 



LXXV. 



LXXVI. 



LXXVII. 



LXXVIII. 



9 



10 

 11 



12 

 13 



14 

 15 

 16 



17 

 18 

 19 

 20 

 21 

 22 

 23 

 24 

 25 

 26 

 27 

 28 

 29 



30 



31 



CO in Vacuum tubes, Red hand thereof, and Scarlet hand, on a 40-foot Spectrum length. 



ii ii Orange hand and Yellow band. 



ii ii Yellow hand and Citron hand. 



n ii Green hand thereof and Blue hand. 



ii ii Indigo hand and Violet hand. 



H in Vacuum tubes, Early Red, Red to Scarlet, region ; on a 40-foot Spectrum length. 



ii ii Orange, Yellow, and Citron. 



ii ii Citron to Green. 



ii ii Green, Glaucous, and Blue. 



ii ii Blue, Indigo, and Violet. 



ii ii Violet continued. 



in Vacuum tubes, Ultra-Red, Red, and Scarlet, regions on a 40-foot Spectrum length. 



ii ii Orange and Yellow. 



ii ii Citron to Green. 



ii ii Glaucous to Violet.. 



N in Vacuum tubes, Ultra- Red regions thereof, adapted to a 40-foot Spectrum length. 



ii ii Ultra Red, Red, and Scarlet. 



ii ii Yellow and Citron. 



ii ii Citron and Green. 



ii ii Glaucous and Blue. 



ii n Blue and Indigo. 



ii ii Violet ; all the above Plates have scales in terms of Wave-number 



per British Inch. 

 Folding Index Map of all the above, and some other, gases, at both high and low tempera- 

 tures, and throughout the visible Spectrum, but greatly reduced in scale. 

 Folding plate of Green CO's extra-green-CH portion ; full size of original record, viz., for 



a 120-foot Spectrum length, with explication of its double arithmetical series. 



Appendix V. On the numerical Wave-number Spectrum Scale adopted here. 



INTRODUCTION. 



After the Royal Society, Edinburgh, had been pleased in 1880 to accept and 

 print my paper on the general appearance of Gaseous spectra as seen on a very 

 small scale, but complete on that scale from one end to the other of the visible 

 spectrum, I was desirous to present them with some very highly Dispersed 

 and much magnified views of the more interesting and probably crucial por- 

 tions of the most important of those spectra. 



An example of acting on that principle had already been set in the admir- 

 able essay of MM. Angstrom and Thalen, published in the Upsala Trans- 

 actions for 1875, For there, both in the Plates and letterpress, the final 

 portions entitled " Mesures Micometriques " are very largely magnified 

 representations of certain small parts of what went before. 



But just as occurred in the earlier division of that great work, so also in 

 this later portion of it, there appeared to me to be too few gases, and too few 

 portions of their spectra treated of, to supply a sufficiently comprehensive basis 

 for this branch of science. 



Neither again in their Mesures Micrometriques did the Dispersion power 

 which those eminent philosophers employed, appear sufficient either in amount 



