590 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



objects, and this increase of the defect, in a national point of 

 view, is to be considered a serious evil. 



The decrease in the acuteness of vision is generally the re- 

 sult of a positive disease of the eye, which may be exception- 

 ally induced at school, while the decrease of endurance arises 

 principally from two causes : the first, a congenital condition, 

 which can be corrected by convex glasses, and can not, there- 

 fore, be the product of school-life ; the second, a disturbance 

 in the harmonious actfon of the muscles of the eye, a defect 

 difficult to cure, generally caused by unsuitable arrange- 

 ments for work. All these three anomalies in vision may 

 arise from the same circumstances namely, insufficient or 

 ill-arranged light, or a wrong position during work, the for- 

 mer obliging us to lessen the distance between the eye and 

 the book while reading or writing, and the same being re- 

 quired if the desks or seats are not in the right position, or 

 of the right shape and size. . 



If the muscles of the eye are not strong enough to resist 

 such tension for any length of time, one of the eyes is left to 

 itself, and while one eye is being directed on the object, the 

 other deviates outwardly, receives false images, and its vis- 

 ion becomes indistinct amblyopic. Or perhaps the muscles 

 resist these difficulties for a time, become weary, and thus is 

 produced the diminution of endurance. 



To prevent these evils the light of the school-room should 

 be sufficiently strong, and should fall on the table from the 

 left-hand side, and, as far as possible, from above. The chil- 

 dren should be obliged to sit straight, and not have the book 

 raised nearer the eye than ten inches. In addition to this, 

 the book should be raised twenty degrees for writing, and 

 forty degrees for reading. Dr. Liebreich thinks that in very 

 few schools are the conditions here stated complied with. 

 He remarks that the proper light is most easily obtained if 

 the class-room is of an oblong shape, the windows being in 

 one of the long sides, and the tables arranged parallel to the 

 short walls, so that the light falls from the left side. The 

 desk of the master should be near the short wall toward 

 which the scholars look. 



This simple and practical arrangement, which in some 

 places is a matter of course, is in England almost exception- 

 al. Light coming from the right hand, according to Dr. 



