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V.—Gaseous Spectra in Vacuum Tubes, under small Dispersion and at low 
Electric Temperature; including an Appendix III., by Prof. ALEXANDER 
S. Herscuet, M.A., Newcastle-on-Tyne. By Piazzi Smytu, F.R.S.E., 
and Astronomer Royal for Scotland. (Read July 19, 1880). 
CONTENTS. 
PAGE 
General Introduction, . : : ; . , 93 
Practical Commencement dbacuibeds ‘ : : 3 / 96 
On the tables of Twenty Gas-Vacuum Tubes, . - 97 and Appendix I. 
Examination of the observed Quantities, and Elimination of fi Te 
purity” Effects, - i 
Search for New Lines and their Gaseous aeabinestions : : 99 and Appendix II. 
Standard Tables of the Principal Gaseous Lines and Bands, . : 99 
Of Changes with Time and Use, . ; ‘ j F ; 100 
On recent observations in Belgium, : - 103 
Of Professor ALEX. S. HERSCHEL’s contribution of ee IIL, ; 104 
ApprenDIx I. Separate Tables of observations of each of Twenty Gases ; pages 105 to 141. 
AppeNDIXx II. Tables of Gaseous Impurities, their characteristics and eliminations ; pages 142 to 149. 
AppEnpDIx III. Professor ALEX. S. HurscHEL’s observations under higher dispersions ; pages 150 to 159. 
Pratt XI. Elemental Gases, first as observed, and then as virtually freed from impurities. (Low 
Dispersion). 
Puate XII. Compound Gases, as observed, and with reference to their dissociations, as well as to unavoid- 
able practical impurities. (Low Dispersion). 
GENERAL INTRODUCTION. 
Of all the various spectra which the progress of experimental science has 
enabled man to observe in the present day, none are so rich, varied, and 
important, as those of gases. And no wonder! for it is only when matter 
has been reduced to the gaseous condition, that it is able to specialise itself and 
write its character with much of its history in any otherwise smooth, undefined, 
continuous spectrum ; while, if in former times, men would have found it an 
impossibility to drive many of the more refractory substances into the state of 
incandescent vapour, what is there now anywhere on the surface of this earth 
which, in small quantity, can resist the action of a powerful and condensed 
induction spark of electricity ; and what application of that spark is so neat, 
elegant, convenient, and economical, as when it is employed in ea aaa with 
so-called gas-vacuum tubes. 
In these tubes the infinitesimally small weight of the inch or two of almost 
VOL, XXX. PART I. P 
