ADDRESS. XCVll 



actually souglit for and found other metals than sodium in the sun by the 

 method of spectrum analysis. His publication of October 1859 inaugurated 

 the practice of solar and stellar chemistry, aud gave spectrum analysis an 

 impulse to which in a great measure is due its splendidly successful cultivation 

 by the labours of many able investigators within the last ten years. 



o 



To prodigious and wearing toil of Kirchhoff himself, and of Angstrom, wc 

 owe large-scale maps of the solar spectrum, incomjjarably superior in minute- 

 ness and accuracy of delineation to any thing ever attempted previously. These 

 maps now constitute the standards of reference for all workers in the field. 

 Pliickcr and Hittorf opened ground in advancing the physics of spectrum 

 analysis and made the important discovery of changes in the spectra of 

 ignited gases produced by changes in the physical condition of the gas. The 

 scientific value of the meetings of the British Association is well illustrated 

 by the fact that it was through conversation with Pliicker at the Newcastle 

 meeting that Lockyer was first led into the investigation of the eftects of varied 

 pressure on the quality of the light emitted by glowing gas which he and 

 Frankland have prosecuted with such admirable success. Scientific wealth 

 tends to accumulation according to the law of compound interest. Every addi- 

 tion to knowledge of properties of matter supplies the naturalist with new 

 instrumental means for discovering and interpreting phenomena of nature, 

 which in their turn aff'ord foundations for fresh generahzatious, bringing 

 gains of permanent value into the great storehouse of philosophy. Thus 

 Frankland, led, from observing the want of brightness of a candle burning in 

 a tent on the summit of Mont Blanc, to scrutinize Davy's theory of fiame, 

 discovered tliat brightness Avithout incandescent solid particles is given to a 

 purely gaseous flame by augmented pressure, and that a dense ignited gas 

 gives a spectrum comparable with that of the light from an incandescent solid 

 or liquid. Lockyer joined him; aud the two found that every incandescent 

 substance gives a continuous spectrum — that an incandescent gas under 

 varied pi'essure gives bright bars across the continuous spectrum, some of 

 which, from the sharp, hard and fast hues observed where the gas is in a 

 state of extreme attenuation, broaden out on each side into nebulous bands 

 as the density is increased, and are ultimately lost in the continuous spec- 

 trum when the condensation is pushed on till the gas becomes a fluid no 

 longer to be called gaseous. Moi-c recently they have examined the influence 

 of temperature, and have obtained results which seem to show that a highly 

 attenuated gas, which at a high temperature gives several bright lines, gives 

 a smaller and smaller number of lines, of sufiiciont brightness to be visible, 

 when the temperature is lowered, the density being kept unchanged. I cannot 

 refrain here from remarking how admirably this beaiitiful investigation har- 

 monizes with Andrews' great discovery of continuity between the gaseous 

 and liquid states. Such things make the life-blood of science. In contem- 

 plating them we feel as if led out from narrow waters of scholastic dogma to 

 a refreshing excursion on the broad and deep ocean of truth, where we learn 

 from the wonders wc see that there are endlessly more and more glorious 

 wonders still unseen. 



Stokes' dynamical theory supplies the key to the i^hilosophy of Frank- 

 land and Lockyer's discovery. Any atom of gas when struck and left to 

 itself vibrates with perfect purity its fundamental note or notes. In a 

 highly attenuated gas each atom is very rarely in collision Avith other 

 atoms, and therefore is nearly at all times in a state of true vibration. 

 Hence the spectrum of a highly attenuated gas consists of one or more 

 perfectly sharp bright lines, with a scarcely perceptible continuous gradation 



