MIRROR 



3842 



MISHAWAKA 



axis, and a ray of light from A striking the mir- 

 ror at M, parallel with the principal axis, is 

 reflected at the principal focus F. The line MF 

 must contain the image of A. Another ray 

 from A passing through the center of curvature 



Construction of an image in a concave mirror. 

 The object is beyond the center, of curvature of 

 the mirror. 



and striking the mirror is reflected back along 

 the same path, CA; this line also contains the 

 image of A. The image is, therefore, found at 

 the intersection of those two lines, namely at 

 A' . In the same way the image of B will be 

 formed at B ' . We see that the image is smaller 

 than the object, inverted, and real. 



In the example shown in Fig. 2 the object 

 was beyond the center of curvature. When the 

 object is situated between the center of curva- 

 ture and the principal focus the image formed 

 is larger than the object, inverted and real, and 

 appears beyond the center of curvature. Re- 

 flectors for carriage lamps, bicycle lanterns, 

 hand shaving mirrors, mouth mirrors used by 

 dentists, all contain concave mirrors. 



A convex mirror is a portion of the outer side 

 of a sphere. The image is formed in the same 

 way as in the concave mirror, but as the center 

 of curvature and the principal focus are behind 

 the mirror, the reflected rays have to be ex- 



Construction of an image in a convex mirror. 



tended also behind the mirror in order to meet 

 these points and to form the image. The image 

 formed in convex mirrors is always behind the 

 mirror, smaller than the object, erect and vir- 

 tual. A polishe^ ball reflects such an image. 



The still waters of ponds and lakes were the 

 only mirrors known to primitive man. The 

 ancient peoples, the Egyptians, the Hebrews, 

 the Greeks and the Romans, used mirrors made 

 of polished metals, such as brass, bronze, silver 

 and gold, and various alloys. Mirrors of glass 

 were first made at Venice at the beginning of 

 the fourteenth century. It was not until 1673 

 that the making of mirrors was started in Eng- 

 land. Mirrors are coated on the back with a 

 metallic covering. Formerly this coating con- 

 sisted of an amalgam of tin and mercury; now 

 silver is used. The silvering is protected by a 

 coat of shellac varnish and on top of this by 

 another coat of varnish that contains red lead. 



Heat, as well as light, is reflected from a mir- 

 ror, and a concave mirror can be used to bring 

 the rays of heat to a focus. Objects can thus 

 be set on fire or melted from a distance by 

 means of reflectors that concentrate the rays of 

 heat upon them. The most famous feat of this 

 kind known in history is that attributed to the 

 Greek mathematician Archimedes, accom- 

 plished during the siege of Syracuse in 213 B. c. 

 It is said that Archimedes burnt the Roman 

 fleet, or a part of it, by employing a set of con- 

 cave mirrors which focused the rays of the sun 

 upon the Roman ships in the harbor. C.R.M. 



MISDEMEANOR, mis de meen' er, an offense 

 of a less serious nature than a felony. Among 

 the offenses so classed are assault and battery, 

 malicious mischief and acts which make the of- 

 fender a public nuisance. The laws of various 

 countries, states and provinces differ, however, 

 in defining such offenses, and what is a misde- 

 meanor in one state may be classed as felony in 

 another. Misdemeanors are usually punishable 

 by fine or brief jail imprisonment. 



MISHAWAKA , mish a waw ' ka, IND., a manu- 

 facturing city, situated in the extreme northern 

 part of the state, about midway between its 

 eastern and western borders, and on the Saint 

 Joseph River. By rail South Bend is four miles 

 west, and Chicago is ninety miles northwest. 

 The Lake Shore & Michigan Southern and the 

 Grand Trunk railroads serve the city; there is 

 also connection with the larger cities of the 

 state by interurban lines. Belgians predomi- 

 nate in the foreign element of the population, 

 which increased from 11,886 in 1910 to 16,385 in 

 1916 (Federal estimate). The city has an area 

 of nearly four square miles. 



Mishawaka has a variety of industrial estab- 

 lishments. Abundant water power is provided 

 for manufactories by the Saint Joseph River, 

 which at this point is spanned by three con- 



