174 



SCIENCE. 



[N. S. Vol. II. No. 33. 



fited and civilization advanced. Grand 

 possibilities lead her votaries on in the hope 

 of still greater achievements than any yet 

 accomplished. The diffusion and advance- 

 ment of scientific knowledge are the objects 

 of the Association for the Advancement of 

 Science. F. W. Putnam. 



Permanent Secretary, A. A. A. S. 



BOLOMETEIC INVESTIGATIONS IN THE 

 INFIIA-BED SPECTRUM OF THE SUN* 



When Sir Isaac ISTewton allowed a beam 

 of light to fall upon a triangular bar of 

 glass, and thus demonstrated the complex- 

 ity of ordinary light, he undoubtedly ren- 

 dered science a great service : but when he 

 stopped there, and said that all transparent 

 substances affected light both qualitatively 

 and quantitatively alike, he did it an injury 

 almost as great. The weight of his word 

 deterred investigators and retarded the 

 development of this branch of optics for 

 very many years. At last it was shown 

 that all transparent substances affect light 

 differently. Some bend all the colors con- 

 siderabljr out of their course, while scatter- 

 ing or ' dispersing ' them but slightly. 

 Others bend, or ' refract,' but slightly, and 

 ' disperse ' considerably. In general the 

 violet is ' refracted ' most, followed by 

 blue, green, yellow, orange and red, which 

 is refi'acted least. Similarly, Newton's ad- 

 vocacy of the theory that light is material 

 ■particles, 'corpuscles,' thrown out from 

 the luminous body, added to the difficulties 

 of gaining a general acceptance of the rival 

 theorj^, which sees in light only a periodic, 

 or ' wave,' motion, in a hypothetical elas- 

 tic medium. To-day every scientist accepts 

 the undulatorjr, or wave, theory of light 

 and is even striving to make it unite the 

 phenomena of light and electricity in one 

 common explanation. 



Long after Newton's corpuscles had 



* Part of a popnlar lecture under the auspices of 

 the New York Academy of Sciences. 



passed out of science, 'caloric,' or the 

 heat fluid, still maintained its list of re- 

 spected advocates, and it remained for the 

 first half of this centurj' to relegate ' ca- 

 loric 'to the curiosity shop along with the 

 ' corpuscles.' Then it was that heat was 

 recognized as another manifestation of those 

 periodic disturbances, or waves, in that 

 elastic medium which was then known as 

 the luminiferous ether, and which is now 

 universally referred to as 'the ether.' In 

 1S02 WoUaston, upon repeating Newton's 

 experiment, discovered certain dark bands 

 traversing the colors and apparently sepa- 

 rating them. Some ten j^ears later Fraun- 

 hofer made these bands the subject of very 

 extensive and careful investigation, observ- 

 ing several hundred and mapping and nam- 

 ing the more important among them. These 

 lines are commonly known now as ' Fraun- 

 hofer lines,' and are used as milestones in the 

 spectrum. Thanks to the labors of WoUas- 

 ton, Fraunhofer, Brewster, Angstrom, Kir- 

 choff, Bunsen and many others in leas de- 

 gree, we know that a chemical element, as 

 sodium, when its vapor is heated sufficiently, 

 will radiate only certain kinds of light; so- 

 dium, yellow; thallium, green; lithium, red, 

 and so on . The 1 ight from any white-hot solid , 

 when passed through a prism, is dispersed 

 into a spectrum having all the colors and 

 no dark lines, that is, a ' continuous spec- 

 trum.' If we put soda in an alcohol flame 

 it will emit j^ellow light, which, being sent 

 through a prism, will not give a continuous 

 spectrum, but onlj' a band of yellow at that 

 place where the yellow would come in a 

 continuous spectrum. Now, if the light of 

 a white-hot solid, electric arc-light, for ex- 

 ample, be caused to pass through the soda 

 flame and then be dispersed into a spectrum, 

 we shall find the latter to be continuous, 

 except for a dark band at exactly that part 

 of the yellow where the soda flame gave a 

 yellow band. The soda vapor in tlie alcohol 

 flame absorbed out of the white light just 



