306 THE FARMER AT HOME. 



it is to be had, in a thoroughly putrescent state, and turned in only 

 to a moderate depth. A dressing also of gypsum, soot, and wood 

 ashes is favorable to the growth of onions ; and we have found neither 

 better than finely decomposed hen-dung. 



OPHIR. In Sacred Geography, the place from which Solomon 

 procured the gold and other precious articles with which he enriched 

 himself, and adorned the temple of Jerusalem. Concerning the part 

 of the world in which Ophir was situated, there have been many and 

 various opinions and conjectures ; some of them extremely fanciful, 

 not to say absurd ; and others supported and elucidated with no in- 

 considerable portion of ingenuity and learning ; still, however, the 

 exact situation of this place is undetermined, though the opinion that 

 it was somewhere either on the eastern or western coast of Africa 

 seems the most plausible, and to obtain the sanction of the most 

 learned and well informed writers, who have discussed or adverted to 

 this point of sacred geography. 



OPTICS. Optics is the science which treats of light, and of the 

 instruments by which it is applied to useful purposes. It is one of the 

 most interesting branches of natural philosophy, but not one of the 

 easiest to understand ; it will be necessary, therefore, that you give to 

 it the whole of your attention. Light, when emanated from the sun, 

 or any other luminous body, is projected forwards in straight lines in 

 every possible direction ; so that the luminous body is not only the 

 centre from whence all the rays proceed, but every point of it may 

 be considered as a centre which radiates light in every direction. The 

 particles of light are so extremely minute, that although they are pro- 

 jected in different directions, and cross each other, yet they are never 

 known to interfere, and impede each other's course. It is still a dis- 

 puted point, however, whether light be a substance composed of par- 

 ticles like other bodies. In some respects, it is obedient to the laws 

 which govern bodies ; in others, it appears to be independent of them : 

 thus, though its course is guided by the laws of motion, it does not 

 seem to be influenced by the laws of gravity. It has never been dis- 

 covered to have weight, though a variety of interesting experiments 

 have been made with a view of ascertaining that point. Some sup- 

 pose that the rays of light, instead of being particles, consist of the 

 undulations of an elastic medium, which fills all space, and which 

 produces the sensation of light to the eye, just as the vibrations of 

 the air produce the sensation of sound to the ear. Most of the phe- 

 nomena may be accounted for by either hypothesis, but that of their 

 being particles applies more happily to some of the facts respecting 

 the modifications of light by refraction and reflection. 



OPIUM. In chemistry and medicine, an inspissated gummy juice, 

 which is obtained from the head of the " papaper somniforum." It 

 is imported from Persia, Arabia, and other warm parts of Asia, in flat 

 cakes, covered with leaves, to prevent their sticking together. It has 



