i>'2 



fully investigated by Fmueuhofer, aud with such exfictnesR that, iu justice, the 

 lines themselves have since received his name, and are now known as 

 " Frauenhofer's lines." Like the term "Bailey's boads," observed on occasions 

 of a solar total eclipse, they have immortalised their investigator, aud show 

 that science is not unjust in distributing her honours amongst her faithful 

 ▼otaries. Several observers had subsequently made more or less successful 

 advances to elucidate the natuie of the dark lines of Frauenhofer, but it was 

 not till so recently as 1839 that these researches received their crowning triumph 

 at the hands of Kirchoff, on whom they conferred a still larger measure of 

 scientific honour and celebrity. I will now quote the words of the address of 

 the President of the Royal Astronomical Society, delivered in February last. 



What Kirchoff did was this : — "In 1859, he propounded as a great natural 

 law, that if a vapour, when sufficiently heated, possesses the property of 

 emitting lights of certain refrangibiUties, that vapour at a lower temperature has 

 a tendency to absorb or refuse a passage to lights of the same refrangibilities 

 which may be incident upon it. Kirchoff demonstrated this law experimentally 

 in thecases of Sodium, Lithium, Strontium, Potassium, Calcium, and Barium. 

 From the vapours of each of these metals he obtained those spectra consisting 

 of intermittent bright lines, and then viewing these spectra through less intensely 

 heated vapours of the same metals, the bright lines became reversed into dark 

 lines. Here, then, we appear to possess a satisfactory explanation of the 

 Frauenhofer dark lines of the Solar Spectrum. The solid or liquid superficies 

 of the sun may be presumed to be incandescent, and hence as a solid or 

 liquid to emit rays of light ranging through a vast variety of refrangibilities. 

 Above this incandescent superficies we may conceive heated vapours of various 

 metals or other ingredients to float ; these vapours will absorb, intercept, or be 

 opaque to rays of light of various refrangibilities, and hence, by this simple 

 process, may arise in the Solar Spectrum the dark lines discovered by Wollaston 

 and Frauenhofer. In order to put this hypothesis to the test, Kirchoff, in 1860, 

 caused a very powerful sjiectroscope to be constructed, so arranged as to permit 

 him to observe the spectra of the vapours of several metals in juxta — or super- 

 position with the Solar Spectrum ; and in this way he identified the bright 

 lines of the vapours of iron, copper, magnesium, and of other substances, with 

 the dark lines of the Solar Spectrum." 



So far as to what Ejichoff did : — "The question at issue was, (continues 

 the address), Do the dark lines which were already well known to exist in the 

 spectra of some of the stars, coincide to so absolute a degree of precision with 

 the bright lines in the spectra of metallic vapours, as to warrant an undoubting 

 belief in the corresponding metallic constituents of the stars themselves? To 

 answer this question it was essential to do what had never been done before, 

 viz., to obtaina juxta, or super-position of the stellar and metallic spectra." 



This was accomplished by two eminent men of science, upon whom the 

 Royal Astronomical Society have, for their discovery, conferred their gold medal 

 for this year, the highest astronomical honour in Europe. By the labours and 



