407 



XXIV. — On the Structure of the Luminous Envelope 



of the Sun. 



By James Nasmyth, Esq., C.E. 



In a Letter to Joseph Sidebotham, Esq. 



Read Marcli 5th, 1861. 



Thinking that it might interest some of your scientific 

 friends to be informed about the remarkable details which 

 I have discovered in the general luminous surface of the 

 sun, as also in the structure of the solar spots, I send 

 you for that purpose a rough but faithful drawing, which I 

 hope may serve to convey a pretty clear idea of the details 

 I refer to. 



In order to obtain a satisfactory view of these remark- 

 able objects, it is not only requisite to employ a telescope 

 of very considerable power and perfection of defining 

 capability, but also to make the observation at a time 

 when the atmosphere is nearly quite tranquil and free 

 from those vibrations which so frequently interpose most 

 provoking interruptions to the efibrts of the observer; 

 without such conditions as I allude to, it is hopeless to 

 catch even a glimpse of these remarkable and delicate 

 details of the solar surface. 



The drawing I send you represents a spot on the sun, 

 which I had a most favourable opportunity of observing 

 on the 20th July i860; although it is in some respects a 

 rather remarkable spot, yet it may be taken as a fair 



