(Arnold), portrait painter, was born at Dort in 1669, and at first was a disciple of Arnold Verbius, a painter of history and portrait. Afterwards he placed himself with Godfrey Schalcken, and continued with that artist for six years. The sweetness of his colouring, and the neatness of his touch, with a striking likeness in his portraits, procured him a number of admirers. He painted in the manner of his master, particularly subjects by candlelight, which were very delicate, and very natural; and much more of his work was requested by the lovers of the art than it was possible for him to undertake. He had the honour to paint the portraits of the Czar of Muscovy; of Frederic I. King of Prussia; of the victorious Duke of Marlborough, as well as many of the princes of Germany; and most of the noblemen who attended the Czar. His style of colouring was extremely good, and he had an elegant manner of disposing the attitudes of his figures; his handling was neat, and the whole had so much harmony that he was justly ranked among the ablest artists of his time. The small pictures of Boonen are in the taste of his master Schalcken; but his excessive application, to answer the multitude of his engagements, impaired his health, and destroyed while it enriched him. He died in 1720.

BOOPTHALMUS, a kind of agate with large circles in it, bearing some resemblance to an ox's eye, from whence it has got this name.