ZOOLOGY. 347 



is composed of three primary colors in the following proportions: yellow, 

 3, red 5, blue 8. The red and yellow rays are the most exciting to the eyes, 

 and in proportion as artificial light possesses them in excess, it is fatiguing 

 and injurious to those organs. The bad effects, however, may be obviated, 

 1st, by surrounding the flame with a chimney tinged pale blue ; 2d, by sur- 

 rounding the light with a shade colored azure blue on the inner side. In 

 these contrivances the color of the light is improved by the addition of the 

 deficient blue rays. 2. Position of the light. A frequent cause of the inju- 

 rious effects of artificial light is the direct and concentrated manner in which 

 it is permitted to fall upon the eyes. No light should be placed in front of 

 the eyes, but it should be either above the head, or rather behind, and on one 

 side, so that the object can be well illuminated, while the eyes are fully 

 protected from the heat and glare. 3. Unsteadiness of the flame. The 

 steadier the flame the better for the eyes ; lights should therefore have glass 

 chimneys to assist combustion and prevent flickering. 4. Heat and dryness. 

 This can not be avoided in rooms heated with hot air, nor where there are 

 many lights ; but it may be obviated by placing in some convenient situation 

 a flat dish containing water ; and those engaged in work requiring a strong 

 light should place a large wet sponge near t^om, to cool and moisten the air 

 by evaporation. It may be also remarked that full blue and green glasses, 

 which are often worn by persons having weak eyes, are highly objectionable, 

 being of definite colors, and exciting complementary colors. Neutral-tinted 

 glasses, being, as the name implies, of no definite hue, screen the eye from 

 all colors alike, and produce an effect most grateful to irritable eyes. 



PEARLS AND PEARL-MAKING IN CHINA. 



The following information respecting the method adopted by the Chinese 

 for facilitating and shaping the growth of the pearl in the pearl-oyster is com- 

 municated to the Journal oftfte London Society of Arts, by Dr. Mac-go wan: 



The practice of the art is confined to two coterminous villages near the 

 district city Tehtsing, in the northern part of Chihkiang, in a silk producing 

 region. In the month of May or June large quantities of the mussel (My tilus 

 cygnus) are brought in baskets from the Tahu, a lake in Kiangsu, about 30 

 miles distant, the largest among the full-grown being specially selected. As 

 their health suffers on the journey they are allowed a few days' respite in 

 bamboo cages in water before being tortured for the gratification of human 

 vanity, when they are taken out to receive the matrices. These are various 

 in form and material, the most common being pellets made of mud taken from 

 the bottom of water-courses, dried, powdered with the juice of the camphor- 

 tree seeds, and formed into pill?, which, when dry, are fit for introduction into 

 the unfortunate subject. Moulds which best exhibit the nacreous deposit are 

 brought from Canton, and appeared to be made from the shell of the pearl- 

 oyster ; the irregular fragments thus procured are triturated with sand in an 

 iron mortar until they become smooth and globular. Another class of moulds 

 consists of small images, generally of Buddha, in the usual sitting posture ; 

 or sometimes of fish. They are made of lead, cast very thin by pouring on 



