34 Dr. Woods on the probable Nature of the Sun's Body. 



which it certainly is, and something more*. When we talk of 

 the apparent rotation of the heavens, we mean that they do not 

 revolve, but only the eai-th, in twenty-four hours all things being 

 replaced. If the earth really revolves in twenty-four hours, it is 

 certain that the oscillation of the pendulum is not in the same 

 direction, and consequently it has rotated, unless any one is 

 absurd enoiigh to maintain that the rotation of the earth itself 

 varies its period at different latitudes. 



I am, Sir, 



Your obedient Servant, 



Alfred Day. 



IV. On the pi^obable Nature of the Sun's Body and on a neiv 

 V Process for rendering Collodion more sensitive. By Thomas 

 ^WooDS, ikf.D.t >J 



THE physical nature of the sun's body, whether it be solid* 

 gaseous, or both, is a matter of doubt to philosophers. 

 The peculiar appearance of the spots and the changes they un- 

 dergo, lead to the supposition that a gaseous envelope surrounds 

 whatever may be the interior ; and Arago's determination, that 

 the sun's direct light is not polarized, renders it probable that 

 the envelope is flame. 



I have lately made some photographic experiments, which 

 may tend further to the establishment of this opinion. It has 

 been long known that the light proceeding from the centre of 

 the sun is more intense than that from the edge. I have taken 

 several pictures of the sun in a camera obscura, by means of a 

 photographic process, exposing the prepared surface of the plate 

 to be acted on for different periods of time. For instance, the 

 Camera being set, and the prepared plate in focus, I have allowed 

 the picture of the sun to fall on it for as short a time as it was pos- 

 sible to uncover and cover again the aperture. I then opened 

 the apei-turc again for a somewhat longer period, having first 

 moved the plate so that another part of it would be acted on. I 

 caused the picture then to fall on another portion of the plate for 

 a longer time, and so on, taking on the same prepared surface 

 iix or eight pictures, each the result of a different length of ex- 



* There is no rotatory teudency in the plane of oscillation, excepting 

 iki so far as this is produced as a result of the earth's constraint on the point 

 of suspension, in other words, the rotatory effect is due to the earth. In 

 this sense it is the eaith's rotation made visible though the angular mo- 

 tion is slower tlian that of the earth ; and the case may be compared to the 

 motion of the box containing? the main-spring of a watch, as evidenced by 

 tbc motions of the hands. ' 



) t Commupicated by the Author. ^ 



