Effect of Bodies on Light and Heat. 407 



of time. Over 70 have been examined by the spectroscope, f of which 

 gave a continuous spectrum showing them to be stars, the other ^ gave 

 the discontinuous spectra characteristic of gases. Nearly all of them. 

 } T ield the three lines shown on the diagram for the nebula in the con- 

 stellation Draco. One of these corresponds with a line of nitrogen, one 

 with the F line of hydrogen, but the middle one corresponds with no line of 

 any known element. The reason no more lines are visible of the hydro- 

 gen and nitrogen, is plain enough when we are told that a sperm candle 

 ^ of a mile away is 20,000 times as brilliant as the nebula. Comets have 

 also been examined. They have given the bright lines of the discon- 

 tinuous or gas spectrum. But what gas, is uncertain, as the spectra are 

 strange. It is something very light. Brorsen's comet, which is 60,700 

 miles in diameter and has a period of 5^- years, but which if solid could 

 probably be put into a flour barrel is, nevertheless, self luminous. The 

 spectrum of Winnecke's comet was found to correspond exactly with that 

 of incandescent olefiant gas, from which it is surmised that its bright 

 lines may be due to carbon. 



One of the most wonderful properties of the spectroscope is its ability 

 to detect movements of bodies towards us or from us. The explanation. 

 is very simple. If a luminous body is approaching us ( or we it ) the 

 waves of light coming from it will reach us in greater rapidity than if it 

 stands still. This will have the same effect as if the waves were short- 

 ened. Now, as we have seen, the shorter waves are refracted most on 

 the spectrum, and so the band that represents those shortened waves 

 will be found to be slightl}' shifted towards the violet end of the spec- 

 trum. On the other hand, if the body is receding from us, the waves 

 will reach us less frequently and the effect will be the same as lengthen- 

 ing the waves. The corresponding lines on the spectrum then will be 

 moved a little toward the red end. 



Lockyer watching the action about a spot in the sun through his spec- 

 troscope has seen the hydrogen line F swaying in one part first toward 

 the red end of the spectrum, then again, after awhile, returning to a 

 straight position, and in another part it would deviate toward the violet 

 end. Sometimes it would be a bright line, at others a dark line. His 

 explanation is, that when the line shifted towards the red end of the 

 spectrum, the cooled hydrogen from the upper solar atmosphere was 

 rushing from us down upon the sun at a fearful rate, which was in some cases 

 38 miles per second. In another part of the spot at the same time, hot 

 hydrogen was rushing up at the same rate, as indicated by the deviation 

 of the line toward the violet end of the spectrum. Still more remarka- 

 ble were Lockyer's observations on a cyclone on the edge of the sun. 

 Here the storm was seen edge- wise, one part going from the observer 

 and the opposite side coming towards him, as shown by the deviation of 



