OP THE LUMINOUS ENVELOPE OF THE SUN. 409 



gives to the general solar surface that peculiar and well 

 known mottled appearance which has for a long time been 

 familiar to the observers of the sun. 



You will note that I consider the penumbra to be a true 

 secondary stratum of the sun^s luminous envelope, and that 

 what is termed the penumbra of a spot is simply a portion 

 of itj revealed to us by the removal so far of the external 

 and most luminous envelope. 



A slight approach to symmetrical arrangement of the 

 details may be observed at the edges of the exterior lumi- 

 nous envelope as it appears surrounding the edge of the 

 spot, and the same may be seen at the edges of the 

 penumbra ; the tendency to symmetrical arrangement 

 being a slight approach to a radial formation ; the fila- 

 ments tending in their general position, at the parts in 

 question, to the average centre of the spot. 



As I have before said, nothing like a tendency to sym- 

 metrical arrangement is observed in the filaments that 

 form the entire luminous surface of the sun. Diagram 

 No. 2 conveys in this respect a very faithful represen- 

 tation. 



I may also here note that, although I have most care- 

 fully watched for it, I have never seen any indication of a 

 vortical or spiral arrangement of the filaments within or 

 about any of the solar spots ; this observation appears to 

 set aside all likelihood of any whirlwind -like action being 

 an agent in the formation of the spots, as has been con- 

 jectured was the case. 



When a solar spot is mending up, as was the case with 

 the one represented in the drawing, these luminous fila- 

 ments, or willow-leaf shaped objects (as T term them), are 

 seen to pass from the edges and extend across the spots, 

 thus forming what I term "the bridges'' or bright streaks 

 across the spots ; if these are carefully observed under 

 favourable conditions, the actual form of these remark- 



SER. III. VOL. I, 3g 



