BUNSEN MEMOEIAL LECTURE. 621 



''The labor expended on the earth's surface in the maintenance of 

 the aninml and vege able creation, and in the i,roduction of geol 4al 

 change, is derived almost exclusivelv from this source ^^^"'-'^''' 



ihoseot the sun's rays which vibrate most slowlv and form the 

 red portion ot the solar spectrum, including the ravs" visible and in- 

 I^nP^Lr f H '^^^^'l^l them, gnve rise by their absorption nK>re 

 especially to the^thermic actions observed on the surface of the earth 

 and m both the fluid zones which as ocean and atmosphere encircle the 

 solid crust of our planet. These rays constitute the sources of heat 

 which m those gi-and processes of distillation and atmospheric dc'posit 

 have eliected these vast transformations of the earth's crust bv the 

 study ot which we obtain some idea of the immensity of the sun's action 

 exerted during- g-e^log'ical ag'es upon our globe. 



''Of a totally difterent kind, on a scai(> less magnificent but not less 

 important, are the effects mainly produced bv the more highlv rcfran- 

 g-ible and more rapidly vibrating portions of the solar rays'. These 

 rays exert the most marked intluence upon the chemical chano-es on 

 which the vegetable world depends, and are thtn-efore of the greatest 

 importance as regards the character and geographical distribution 

 of organic nature. 



"Although the atmospheric phenomena regulating the amount and 

 distribution of the chemical action of light on the earth's surface have 

 not as yet been systematized to the same extent as the thermic, elec- 

 trical, and magnetic phenomena of meteorology, the reason is not so 

 much that their importance has been overlooked, as that theditliculties 

 which surround an exact investigation of the subject have up to the 

 present time proved insurmountable. * * * The light which tlie 

 sun radiates into space during each minute of time represents a chem- 

 ical energy, by means of which more than twenty-tive and a half 

 billions of cubic miles of chlorine and hvdrogen mav be combined to 

 form hydrochloric acid." (Phil. Trans.," 1859 (1-I9).*87l>.) 



Of all Bunsen's researches, the one which will undoubtedly stand 

 out preeminent as time rolls on is that on spectrum analysis. 



The most important discovery made by Bunsen dui'ing (In- >lioi-t 

 duration of his residence in Breslau was the disco\'erv of Kiiclihoir, 

 who was then professor of physics in that university, and whose g!-eat 

 abilit}^ the elder man at once recognized. No sooner had Jolly re- 

 moved to Munich in 185-t than Bunsen to )k care that Ivirchholl" should 

 be his successor in the Heidelberg chair of physics. And thus came 

 about that great twin research which_has made the names of tlicsc men 

 known through the Avide world. To dilate upon th(> importance of the 

 discov^ery is unnecessary; to follow out the growth of this brane'i of 

 science in its height and depth and breadth is here impossil)le. All 

 that can be now done is to indicate briefly the origin of the dis.-overy 

 and to refer to a few points in Bunsen's work which are of special 

 interest to chemists. To begin with, let me give you in Bunsen's own 

 words the account of Kirchhoff's great discovery— namely, the fidl 

 explanation of FraunhofVr"s lines in the solar spectrum, pointing tin- 

 way to a knowledge of the chemical composition of the sun and lixed 



