CYCLOPES 



1680 



CYLINDER 



temperature, and they originate in areas that 

 have low atmospheric pressure. In the vertical 

 system of atmospheric circulation the sur- 

 face air, which is warmed by the heat radiated 

 from the earth, is constantly ascending, while 

 the colder air above is constantly descending. 

 When in any locality there is a period of calm 

 this vertical circulation of the air is arrested, 

 and the result is a condition of unstable equi- 

 librium. In other words, a heavy stationary 

 layer of cold air overlies a surface layer of 

 warm light air. When finally the air is set 

 in "motion by a current from without, the cold 

 air rushes downward and there is an inflow from 

 all the surrounding areas. This inflow .moves 

 in a spiral direction, with a gradual increase 

 of intensity, and when it reaches the upper 

 regions of the air the moisture is condensed, 

 clouds form and rain often falls. The cyclonic 

 disturbance has two movements the rotating 

 whirl toward the center of low pressure and 

 the forward movement of the entire storm. 



Nearly all land storms are of. a cyclonic 

 nature, but many of them are so mild that 

 their rotary motion is not noticed by any except 

 trained observers of the Weather Bureau. 

 These storms travel in the direction of the 

 prevailing winds; the spiral whirl of cyclones 

 in the northern hemisphere moves in the 

 opposite direction from that of the hands of 

 the clock, and in the southern hemisphere in 

 the reverse .direction. North of the equator 

 the movement is first toward the northwest 

 and then toward the northeast. In the south- 

 ern hemisphere it is southwest, then southeast. 

 The corresponding movements towards centers 

 of high pressure, in which the currents of air 

 flow spirally from the central area outward, 

 are called anticyclones. The central area of 

 an anticyclone is an area of clear skies and 

 fair weather. 



Related Subjects. The following articles In 

 these volumes will make more clear the general 

 principle of a cyclonic disturbance and the dis- 

 tinction between various types : 

 Barometer Tornado 



Hurricane Typhoon 



Storms Whirlwind 



See, also, WIND, and the topics listed there. 



CYCLOPES, siklo'peez, in Grecian legend, a 

 race of giant shepherds. Each had only one 

 eye, which was placed in the middle of the 

 forehead. These giants dwelt in Sicily. In the 

 story of Hesiod they were the sons of Uranus 

 and Gaea, or Heaven and Earth, and were slain 

 by Apollo for having furnished Zeus with thun- 

 derbolts to kill Asclepius. See MYTHOLOGY. 



CYLINDER, sil'inder. A circular solid hav- 

 ing the same diameter throughout its length, 

 and having as its ends two equal parallel circles, 

 is called a cylinder. These circles are called 

 the bases of the cylinder; the distance between 

 the bases is the altitude 

 (a-a) of the cylinder; 

 the curving surface is 

 called its lateral, or con- 

 vex, surface ( Fig. 1 ) . 



We see this figure in 

 water pipes, gas pipes, 

 logs, iron rods, tin veg- 

 etable cans, water tanks 

 and so forth. 



From a rectangular 

 piece of tin or paper 

 six inches long and four 

 inches wide you can 

 make a cylinder six 

 inches in circumference 

 and four inches high, 

 allowing no material fdr 



a lap (Fig. 2). From 



... Y. . x , J (a-a) Altitude; (6) 



this it is seen that the perimeter of base; (c) 



lafpral siirfWp nf a rv! diameter of base; (rf) 

 lateral surtace ol a cyl- ]ateral sur face of cyl- 

 inder is equal in area inder. 

 to a rectangle whose length is equal to the cir- 

 cumference of the cylinder and whose width is 

 equal to the altitude of the cylinder. 



FIG. 1 



6 inches 



FIG. 2 



Showing the relation between the area of the 

 lateral surface and that of a rectangle of similar 

 dimensions. 



Therefore we have this law: Area of lateral 

 surface of a cylinder is the product of the 

 circumference anjl the altitude when these two 

 dimensions are expressed in the same linear 

 units. For example: Find the lateral surface 

 of a water pipe whose circumference is 30 

 inches, and whose length is 20 feet. Solution: 

 lateral surface in square feet=20X2 1 /& :: =50, or 

 lateral surface in square inches=240X 30=7200. 



If we know the diameter or radius, and the 

 altitude of a cylinder, to find its lateral sur- 

 face, we first find the circumference and pro- 

 ceed as before. Circumference equals 3.1416 

 Xdiameter or 2X3.1416Xradius (see CIRCLE). 

 For example: Find how many square inches 

 of tin in the lateral surface of a can 3 inches in 



