MICROMETER 



3791 



MICROSCOPE 



The growth of the commercial and industrial 

 interests of Michigan City is due to its shipping 

 facilities. Iron ore, salt, lumber and farm prod- 

 ucts are the chief articles of trade, and the 

 manufacturing interests are represented by lum- 

 ber mills and furniture, chair, hosiery and knit- 

 goods factories. All of the railroads serving the 

 city have big machine shops here. Michigan 

 City has a United States life-saving station, 

 the Northern Indiana state prison, a public li- 

 brary, a soldiers' monument and a large amuse- 

 ment park on the lake front. Of special inter- 

 est to visitors are the great sand dunes which 

 have been heaped upon the lake shore west of 

 the city. 



MICROMETER, mi krom' e ter, an instru- 

 ment used in connection with a microscope or 

 telescope for measuring very small distances. 

 The name is derived from the Greek word 

 mikros, meaning small, and metron, meaning 

 measure. The 

 simplest form of 

 micrometer con- 

 sists of a fine scale 

 marked on a glass 

 disk in hun- 

 dredths of an inch 

 to form squares; 

 the observer is 

 enabled to deter- 

 mine the size of 

 the object by the number of squares covered. 

 Surveyors' instruments have micrometers at- 

 tached which measure distances by means of a 

 screw with a very fine thread, and there are 

 also special forms for the accurate measure- 

 ment of V-threads on bolts and screws. An- 

 other special form is used to measure star dis- 

 tances on photographic plates. 



MICRONESIA, mikrone'shia, a name ap- 

 plied to a division of Pacific islands lying be- 

 tween the Philippines on the west and the 180th 

 meridian. The group is one of the four divi- 

 sions of Oceania. For location and names of 

 the islands of Micronesia see colored map ac- 

 companying the article OCEANIA. 



MICROSCOPE, mi'kroskope, from two 

 Greek words, mikros, meaning small, and sko- 

 pein, meaning to view, is the name applied to 

 an instrument for magnifying small objects. 



Simple Microscope. This is commonly called 

 a magnifying glass; it consists of a stationary 

 double-convex lens to be held between the 

 object and the eye. It is very useful for exam- 

 ining flowers, insects, etc., and is a familiar ob- 

 ject in the high school biological laboratory. 



MICROMETER 

 Used by surveyors. 



The most powerful simple magnifiers have a 

 magnifying power of twenty diameters; that is, 

 they are capable 

 of making the 

 surface of an ob- 

 ject examined 

 appear 400 times 

 larger than it 

 really is. The av- 

 erage microscope, 

 however, has a 

 power of from 

 five to ten diam- 

 eters. The sim- 

 ple microscope 

 has been in use A SIMPLE MICROSCOPE 

 for centuries. In With glass slide for ob J ects - 

 the ruins of Nineveh was found a lens of rock 

 crystal that had been used as a magnifier by 

 the ancient As- 

 syrians thousands 

 of years ago. 



Compound Mi- 

 croscope. This 

 instrument has 

 for its essential 

 parts an object 

 glass and an eye- 

 piece. These are 

 mounted in tubes 

 so adjusted that 

 the tube contain- 

 ing the eyepiece 

 slides within the 

 one which holds 

 the object glass. 

 The tubes are 

 attached to a 

 stand, the latter 

 containing a plat- 

 form for holding COMPOUND MICROSCOPE 

 the object. Be- 

 neath the plat- < 2 > 

 (3) 



(1) Coarse adjustment by 

 rack and pinion 



Micrometer head of fine 

 adjustment 



Fine adjustment pillar 



(4) Inclination point 



(5) Pillar 



(6) Arm 



(7) Clips 



(8) Eyepiece 

 ... ( 9 ) Draw tube 



A magnified QO) Body tube 



image of the ob- 

 jeet is formed by 



form is a small 

 convex mirror for 

 reflecting light 

 upon the object. 



<JJ| 

 a.) 



the object glass, (is) Focusing screw 

 and a magnified <}?> }g Si 



image of this (18) Mirror 



(19) Horseshoe base 

 image is formed 



by the eyepiece. The apparent size of the ob- 

 ject is increased or reduced in proportion as the 



