SPECTRA OP SOME OP THE BRIGHTER STARS. 
723 
Table A, Sub-division y, 2 1 
' ^(jroup iV 
)) !) y? 1J 
,, B, 
. C, 
7> 
a, 5 
CL, 4 
CL, 3 
a, 2 
GL, 1 
CL 
> Group III. 
a Group II,. 
It will be seen that the sequence now determined from the photographs follows 
exactly the same order as the groiq^s originally suggested by the hypothesis, from a 
discussion of the eye observations. That is, it is not necessary to interchange any of 
the groups in order to obtain agreement with the photographic results. 
The Hottest Stars. (Group IV.) 
At this point it becomes necessary to consider what spectra shall be included in 
Group IV. In the Bakerian Lecture I wrote as follows with regard to it :— 
“ The next group, the fourth, brings us to the stage of highest temperature, to 
stars like a Lyrse ; and the division between this group and the prior one must be 
more or less arbitrary, and cannot at present be defined. One thing, however, is 
quite clear, that no celestial body without all the ultra-violet lines discovered by 
Dr. Huggins can claim to belongf to it.” 
We are met by a similar difficulty when we attempt to draw the dividing line 
between this group and the next (Group V.). 
The photographic spectra, however, enable us to more clearly define the group, and 
it will be convenient to include the stars of Table A, Sub-division y, 1 ; Table A, 
Sub-division y, 2 ; and Table A, Sub-division 8. The stars in the first of these sub¬ 
divisions are still increasing their temperatures, though having almost reached their 
maximum, and they are distinguished from stars of Group III. by the reappearance 
of the line at X 448, and in having broader hydrogen lines than those stars. 
The stars of Table A, Sub-division y, 2, represent, so far as we can judge at present, 
the stars of highest temperature. They are distinguished from those of the previous 
sub-division by the disappearance of the line at X. 
Stars of Table A, Sub-division 8, which include a Lyrse and Sirius, are marked by 
the appearance of mon lines in the spectrum. They probably represent the earliest 
stage of cooling. 
4 z 2 
