56 



composed of these objects ; and No. 3, a large drawing of a 

 solar spot as seen on the 20th of July, 1860, exhibiting the 

 surface of the sun composed of these objects, as also the 

 penumbra and the bridges across the dark portion of the spot 

 in which the exact shapes of these objects were to be seen most 

 clearly. 



Mr. Sidebotham stated that the image of the sun was 

 examined by Mr. Nasmyth with a mirror of plane glass, set 

 at an angle of 45 degrees ; nearly the whole of the light and heat 

 of the sun passed through the glass, and the rays used were 

 those only reflected from its surface. 



Mr. Charles O'Neill read a Paper " On Changes of 

 Density which take place in Rolled Copper by Hammering 

 and Annealing." 



The results of his experiments proved that the best com- 

 mercial rolled copper actually lost density by hammering 

 instead of gaining as might have been anticipated. In the 

 first series of experiments, ten pieces of copper were cut from 

 a sheet of the thickness of i% inch, the pieces weighed from 

 250 to 320 grains each, their mean density was 8'879. The 

 pieces were then separately subjected to the action of a 

 powerful compressing machine, acting on the principle of the 

 genou, about fifty blows being given. The density of these 

 hammered pieces showed a mean of 8*855, being a loss of 

 0-024. The same pieces were annealed by being placed in 

 red hot sand, and cooled slowly ; when cleared from adhering 

 oxide, the mean density was found to be 8*884, being an 

 increase of 0*029 on the hammered pieces, and 0*005 on the 

 original pieces. A second series of experiments, made with 

 very great care, corroborated the first in the main points. 

 The pieces were from another and better sheet of copper; 

 ten pieces, weighing each from 420 to 520 grains, showed a 

 mean density of 8*898, being hammered by the same machine ; 

 their mean density became 8*878, showing a loss of 0*020 by 



