Note on the Spectritni of Silicium. 



451 



1. 



i r 



3. 









* 1 







1. SiF 4 vacuum tube (capillary). 



2. Si0 2 spark with Spottiswoode coil. 



3. Vacuum tube (bulb) Si0 2 spark with small coil. 



The accompanying figure shows the behaviour of the different sets 

 A, B, and C in the spectra of j3, y, £ Orionis. 



I 



I 



1. £ Oriouis. 



2. y Orionis. 



3. /3 Orionis. 



We find that set A is most prominent in the spectrum of ft Orionis, 

 that set C predominates in the spectrum of y Orionis, and that set B is 

 by far the strongest in that of £ Orionis. 



That the stars named represent three different grades of tempera- 

 ture, £ Orionis being the hottest, and /3 Orionis the coolest, has been 

 previously deduced by the discussion of other lines in their spectra. 

 This result was embodied in a paper " On the Order of Appearance 

 of Chemical Substances at different Stellar Temperatures," which I 

 read to the Society in February of the present year. In that paper 

 a, Crucis was given as a typical star representing a stage of tempera- 

 ture between those of p Orionis and f Orionis. That star can be very 

 well replaced for the purpose of the present discussion by y Orionis, 

 the two spectra being nearly identical. 



The line at X 3905*8 previously mentioned as occurring in both arc 

 .and spark spectra, is not represented in the spectra of any of these 

 stars. It is possibly present in the spectra of stars like the sun, as 

 Eowland records it in his " Preliminary Table of Solar Spectrum Wave- 

 lengths," as being coincident with the well-marked Fraunhofer line 

 .at X 3905*660. This coincidence, however, is open to doubt; from a 

 .comparison of the Eowland grating photographs of the silicium spark 



