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THE POPULAR SCIENCE MONTHLY. 



tack of measles, scarlet fever, diphtheria, 

 ■whooping-cough, or from any one of the 

 depressing diseases of childhood, unable to 

 study as they did before the attack. A weak- 

 magnifying spectacle, by helping the mus- 

 cles to do their work, will enable such chil- 

 dren to continue their studies till tonics daily 

 administered restore the needful strength 

 to the enfeebled muscles. The foregomg 

 statements are based upon perfect eyes. 

 Unfortunately, the eyeball, with the many 

 other features, has not always the perfec- 

 tion of symmetry. Near-sighted long eyes 

 and over-sighted flat eyes are the common 

 deviations from the standard shape. In the 

 near-sighted eye, called myopic^ the eye is 

 so long from front to back that the lens is 

 too far from the retina. The result is, that 

 rays of light from a distant object come to 

 a focus, and have begun to diverge when 

 they reach the retina, so that the image 

 formed is blurred. The second deviation 

 in the form of the eye is called hyperopia. 

 This is a flat eye, a very common form in 

 children. It is a congenital defect, in which 

 the crystallme lens is located so near the 

 retina that light, passing into the eye, is 

 stopped by the retina before it comes to a 

 focus. This must also produce an iil-defined 

 picture. Unfortunately, faulty eyes, which 

 give out under use, do not appear differently 

 from perfectly shaped ones. The flatten- 

 ing, or the elongation, is not in the exposed 

 cornea. It is usually at the expense of the 

 inner half of the eyeball, hid away in the 

 socket. If children, either by inheritance 

 or acquisition, have misshaped eyes, so that 

 they can not see objects clearly through the 

 usual range of distances, what can be the 

 propriety of allowing them to go through 

 life as if in a constant fog, when a properly 

 selected glass clears up the mist, and enables 

 them to see as others do ? 



Fresh- Water Pearls. — The cultivation of 

 the pearls of fresh-water mussels has be- 

 come an industry of considerable importance 

 in Saxony and other parts of Germany. The 

 pearls are generally inferior to those of the 

 genuine pearl-oysters, but occasionally a 

 gem of real excellence is produced. Some 

 very fine settings of such were exhibited at 

 the Exposition in Berlin. The Venetians 

 carried on this branch of trade to a con- 



siderable extent during the middle ages, and 

 controlled it till 1621, when the Elector of 

 Saxony also undertook it, at the suggestion 

 of Moritz Schmirler, a draper of Oelsnitz, 

 and appointed Schmirler "first pearl-fisher." 

 Schmirler was succeeded on his death by his 

 son, and the business has contin\ied in the 

 family to the present day, under the su- 

 perintendency of the forestry department, 

 which has also to do with the waters of the 

 region. The pearl-hunting is carried on in 

 the spring, as soon as the water is warm 

 enough to wade in for hours continuously. 

 The mussels are examined by means of an 

 instrument, by which the shells can be 

 opened enough to see what is within them 

 without hurting the mollusks. If they con- 

 tain well- developed pearls, they are sacri- 

 ficed ; if not, they are returned to the beds. 

 The same beds are not usually gone over 

 again for several years. Experiments made 

 in the Elster, in the artificial production of 

 pearls, have not met with much success. A 

 wound in the mouth of the mollusk will 

 lead to the deposition of the calcareous 

 rhatter, but it is uncertain whether it will 

 be of common shell-matter or of pearl — 

 and upon this all the value of the operation 

 depends. In the Dutch East Indies, the 

 formation of pearls in the pearl-oyster is 

 sometimes provoked by inserting a grain of 

 sand within the shell. A considerable busi- 

 ness is done at Adorf in the manufacture 

 of articles of fancy from the nacre of mus- 

 sels. 



Geological SnrTcy of Palestine. — Pro- 

 fessor Hull has just made a successful geo- 

 logical survey of Palestine, preparatory to 

 the construction of a geological map of the 

 country. He has traced the ancient margin 

 of the Gulfs of Suez and Akabah to a height 

 of two hundred feet above their present 

 level, so as to show that the country has 

 been submerged to that extent and has been 

 gradually rising; and he believes that at 

 the time of the Exodus a continuous connec- 

 tion existed between the Red Sea and the 

 Mediterranean. The Dead Sea appears to 

 have formerly stood at a height of fourteen 

 hundred feet above its present level, or 

 about one hundred and fifty feet above the 

 level of the Mediterranean. Evidences of a 

 chain of ancient lakes have been found in 



