

! 



Miscellaneous Intelligence. 443 



as the product resulting from the decoction of pure chicory does not 



strike a blue color* 



IV. Adulteration with roasted acorns, which may be detected by 

 iodine-water and by persulphate of iron, which in such a case strikes a 

 black color. 



V. Adulteration with roasted corn, haricots and peas may be delected 

 by means of iodine-water. 



There is no method as yet known of detecting the adulteration by 

 roasted beet-root and carrot. 



7. On an unnoticed kind of abnormal vision ; by Prof. C. Dewey. 

 There are two well known kinds of abnormal vision in eves not 

 iseased, the far-sighted, and the wear-sighted. The former occurs 

 in good eyes, as persons advance in life, beginning about the age of 

 forty, and is remedied by plane, or better, by convex spectacles. The 

 latter is found in youth or young persons, and finds its remedy in con- 

 cave glasses. The far-sighted are unable to see near and small objects, 

 and remove them at an inconvenient distance, while they see remoter 

 objects perfectly well without glasses. The near-sighted are unable to 

 see small objects unless they are brought inconveniently near, and 

 have no distinct vision of remote objects. 



There is a kind of abnormal vision, different from either of these, 

 which is not far-sighted nor near-sighted, but in which near small objects, 

 or larger distant objects, are not seen with distinctness. This imper- 

 fection occurs in children and young persons, and is remedied by con- 

 vex spectacles which are suited to the eyes of persons from sixty- five 

 to seventy years of age. The younger eyes require the older glasses, 

 and with advancing years less convex glasses are required. At the age 

 of forty-five or more, this kind of abnormal vision becomes much di- 

 minished. 



As the young use the glasses of the farsighted, this kind may be 

 called neo-macropia. It is evident that convex glasses produce that 

 change in the rays of light which fits such eyes to see distinctly small 

 and large objects at varying distances. This fact proves that there is 

 no defect in the adjusting power of the eyes. 



The cause then is to be sought in the structure of the eye. As this 

 kind of eyes does not appear to be too much or too little convex, and 

 as the image is not formed soon enough in the eye or is too far back, 

 either or all of the three following may be the cause : 1, too little con- 

 vexity of the crystalline lens, or 2, its position too near the retina, or 3, 

 its too little density. The second is the probable cause. Spectacles 

 sufficiently convex would bring the rays to a focus, let either or all of 

 °f the three causes operate, and with the usual adjusting power of 

 the eye give distinct vision for near or remoter objects. 



Though this kind of abnormal vision seems not to have attracted at- 

 tention, "for I have found but one al/usion to h w consulting authors 

 on optics, it is relatively common. In New England and New York, 

 more than fifty instances of it have come to my knowledge in the five 

 °r six years past. A child of fifteen was able to see distinctly for 

 the first time by the use of his grandfather's spectacles. A young 

 man of eighteen required convex glasses of ten inch focus, while per- 

 sons of seventy years use those of fourteen to eighteen inch focus. 

 Children often make little progress in study, because they do not see 





