SKETCH OF WILLIAM HUGOINS. 263 



Roberts of this nebula shows a planetary system at a somewhat 

 advanced stage of evolution ; already several planets have been 

 thrown off, and the central gaseous mass has condensed to a mod- 

 erate size as compared with the dimensions it must have possessed 

 before any planets had been formed." In 1891, after more defi- 

 nitely describing the appearance of Mr. Roberts's photograph, he 

 said that "to liken this object more directly to any particular 

 stage in the formation of the solar system would be f to compare 

 great things with small,' and might be indeed to introduce a false 

 analogy ; but, on the other hand, we should err through an excess 

 of caution if we did not accept the remarkable features brought 

 to light by this photograph as a presumptive indication of a prog- 

 ress of events in cosmical history following broadly upon the lines 

 of Laplace's theory." 



Dr. Huggins's spectrum observations on comets, in connection 

 with those of other observers, satisfied him of the existence of 

 different types, and that the same comet might present on one 

 occasion one spectrum and on another the other spectrum ; that 

 they shine partly by reflected solar light and partly by their own 

 light, the spectrum of which indicates the presence in the comet 

 of carbon, possibly in combination with hydrogen. In the case 

 of the Wells comet of 1882, he remarked that as Prof. A. Herschel 

 and Dr. Von Konkoly had showed long before that the spectra of 

 the periodic meteors are different for different swarms, it was not 

 surprising that we now had a comet the matter of the nucleus of 

 which under the sun's heat showed an essential chemical differ- 

 ence from the long series of hydrocarbon comets which had ap- 

 peared since 1864. The spectrum of Coggia's comet (1874) indi- 

 cated an approach to the earth of forty-six miles per second, 

 while the real velocity of approach was only twenty-four miles 

 per second. It was uncertain whether the whole or part of the 

 difference in the velocity was due to the motion of the matter 

 within the comet. It seemed probable, therefore, that the nucleus 

 was solid, heated by the sun, and throwing out matter which 

 formed the coma and tail ; and part of this was in a gaseous form, 

 giving the spectra of bright lines. The other portion existed 

 probably in small incandescent particles ; the polariscope show- 

 ing that certainly not more than one fifth of the whole light was 

 reflected solar light. In a paper on Photographing the Solar 

 Corona without an Eclipse, Prof. Huggins spoke, in 1882, of prob- 

 lems of the highest interest in the physics of our sun connected 

 with the varying forms of the coronal light which seemed to 

 admit of solution only on the condition of its being possible to 

 study the corona continuously, and to confront its changes with 

 other visible phenomena presented by the sun. The spectro- 

 scopic method of viewing the prominences failed ; experiments in 



