168 



UNDULATOUY FORCES. LIGHT. 



[SPECTRUM AN.U.\ sis. 



when unoorabinod furnish. Aqueous vapour alway* givus 

 the bright lino* duo to hydrogun, and hydrochloric acid 

 the mixed system of line* which would be produced by 

 incandescent hydrogen and chlorine. 



" There is obviously a marked difference between the 

 effect of intern ignition upon iuu>t of the metallic and 

 non-meUllio bodice. 



'The observations of PI itaker upon the spectra of i. xlino, 

 bromine, and chlorine, thow that they give, wheu limited, 

 a very different series of band* to those which they 

 funiuh by absorption, as Dr. Gladstone lues already 

 pointed out ; but it is interesting to remark, that iu the 

 cue of hydrogen, which, chemically, is so like a metal, 

 we have a comparatively simple spectrum, in which thu 

 three principal bright lines correspond to Frauuhofer's 

 dark lines, C, F, and G (1'lucker). It is, however, to be 

 specially noted, that hydrogen occasions no perceptible 

 absorption bands at ordinary temperatures in such thick- 

 nesses as we can command in our experiments ; aud the 

 vapour of boiling mercury U also destitute of any 

 absorptive action, although mercury, when ignited by 

 the electric spark, givesacharacteristic aud brilliant series. 



" The following experiment suggested itself to the 

 author as a direct test of Kirchkotf s theory : Two gas- 

 burners, into which were introduced chloride of sodium 

 on the wick of a spirit-lamp, were placed so as to 

 illuminate equally the opposite sides of a sheet of paper 

 partially greased ; the rays of the electric light, screened 

 from the photometric surface, suitably protected, were 

 made to traverse one of the flames. If the yellow rays 

 of the light were absorbed by the sodium flame, the light 

 emitted laterally by the flame should be sensibly increased. 

 The experiment, however, failed to indicate any such 

 increase in the brilliancy of the flame, tiossibly because 

 the eye U not sufficiently sensitive to detect the slight 

 difference which was to be expected." 



Ki. m a perusal of the interesting facts contained in 

 the preceding remarks and experiments, our readers 

 will perceive that eve. y solid body, when brought into a 

 state of rapour and incandescence, produces definite and 

 decided effects in reference to the bands of the spectrum. 

 Each body, i" fact, has a spectrum of its own ; the 

 perfection and constant identity of which is preserved, 

 provided no o* hur interfering cause be present. < 

 precautions, IIOWCV;T, are required in performing the 

 experiments, iMjXH-ially by those persons who may not be 

 accustomed to delicate investigations. Even solid but 

 invisible bodiiis floating in the atmosphere may invalidate 

 the result ; aud, under certain circumstances, the minute 

 portion of common salt often present in the air, has pro- 

 duced a spectrum, of the sodium kind, much to the 

 perplexity of tin observer. It must be borne in mind that 

 the new methai of analysis is so excessively refined 

 and exact, that .'.rtry possible precaution may fail in 



affording results which might be expected ; and sub- 

 stance* in i>n>|><>rtiiins " small as to defy all other HUMUS 

 t.vti..n, may intrude themselves, and so modify 

 the spectral appearances. 



The spectrum analysis has been extensively investi- 

 gated and employed by many eminent observers ; and 

 its indications have been used in numerous branches of 

 research in various departments of optical science. All 

 luminous bodies may be examined by it ; and if the 

 results are compared with certain standards previously 

 obtained, inferences may be drawn with respect to the 

 colour of light and its cause, which would be utterly 

 unattainable by any other means. For instance, much 

 dispute respecting the nature of the solar rays and atmo- 

 sphere has been prevalent, and numerous theories have 

 been advanced to account for the production of both the 

 hc.it and light of the sun. By means of the spectrum ana- 

 lysis, however, Professor Airy, the Astronomer Royal, 

 does not hesitate to affirm that the surface of the sun is in 

 a state of strong incandescence ; that immense bodies of 

 vapour are constantly arising therefrom ; and even the 

 spectrum produced by iron in the state of vapour has 

 been distinctly noticed in the solar light. 



In a similar manner, the light of the planets, fixed 

 stars, comets, <tc , is readily examined, aud compared 

 with that of the solar rays. A new means of investiga- 

 tion is thus put into the hands of the philosopher. The 

 astronomer, the mathematician, and the chemist, are thus 

 jointly called in to determine some of the most interesting 

 problems of astronomy. The theories and facts of each 

 branch of science are thus correlated ; the deductions of 

 each are checked or modified by each other ; and both the 

 chances and sources of error are diminished in a wonderful 

 and satisfactory manner. 



To those of our readers who may be desirous of re- 

 peating the experiments, we may mention, that complete 

 apparatus for the purpose is now made by the leading 

 philosophical instrument-makers in London, in which 

 all the requisite miuutiaa of construction, Arc., are fully 

 attended to. This method of analysis is, therefore, 

 within reach of any one possessing a tolerable acquain- 

 tance with optical and chemical science ; and will 

 doubtless prove a source of extensive discovery in 

 physical science generally. 



Like all new inventions, its use may at first lead to 

 crude and indigested theories. In the hands of many 

 observers, however, that evil will meet with its own 

 correction ; and as soon as a sufficient number of facts 

 has been collected, we shall be able to make safe de- 

 ductions. It is more than likely that the spectrum 

 analysis will prove, in a physical point of view, as 

 beneficial and useful an adjunct as did the invention of 

 fluxions, or the differential calculus in the mathematical 

 department of astronomy and allied sciences. 



