M. Arago on Nehulw, 307 



would answer well in this country for theuppcr parts of garden- 

 walls, and generally for building when strength is not re- 

 quired. 



The roofs of dwelling-houses are commonly flat, and formed 

 of poplar- trees, neatly peeled — small laths are placed across 

 the beams, and a coarse mat, made of reeds, is placed on the 

 top ; a layer of furze is laid over the mat, and the whole is 

 covered by a considerable thickness of clay ; the top of the 

 clay is gently sloped, and rendered impervious to watei', by 

 being coated repeatedly with clay and chopped straw. 



In the houses of the wealthy, the roof is lathed and plastered 

 in the inside, and often beautifully painted and gilt. 



The walls of inferior houses are plastered with clay and 

 chopped straw, which has a neat clean appearance ; while the 

 apartments of the rich are beautifully finished with stucco, 

 which is either left plain, or decorated with gilding and 

 painting. 



It is unnecessary to narrate the arrangement of Persian 

 houses, as good descriptions of these are to be met ^vith in 

 the works of recent travellers : and the writer has throughout 

 limited his observations to such processes as have not been 

 hitherto noticed. 



On Nehuloe. Bv M. Arago.* 



•' 



Definitions, — The above is the name applied to the diffused 

 spots which astronomers have discovered in all parts of the 

 heavens. These spots or lights appear to depend on two en- 

 tirely different causes, of which it is necessary to give some 

 brief explanation. 



The stars are very unequally scattered through the firma- 

 ment. In certain regions they are crowded ; elsewhere we 

 may traverse very extensive spaces, either with the eye or 

 with a glass, without perceiving one. This general want of 

 uniformity in the richness of the starry heavens, has not been 



♦ From the Historical and Critical Analysis of the Life and Works of 

 Sir William Hcrschel, in ih.^ Annuairc pour fan 1842, i^rescnU an B&ipar Ic 

 Bureau dcs Longitudes. 



