DEFINITION OF TERMS. 



155 



consist of 4 arms and the sails connected 

 to those arnns at one edge, so as to yield to 

 the force of wind, and the elasticity of the 

 sails bring them up to the wind again 

 whenever its force abates, (this is the 

 more necessary as engineers are not 

 agreed upon the proper angle of the sails 

 with the wind's course,) the idea may 

 be formed by the manner in which the 

 feathers of birds are acted on by the wind. 

 The mill may be stopped by a rod made 

 to extend through the axis from one end 

 to the other, so that when the arms are 

 attached to one end by a cord or cogs, 

 and power applied to the other end of 

 the rod the sails may be turned with one 

 edge to the course of the wind; that is 

 in a line parallel with the axis of the 

 wheel. 



This rod may be moved by the person 

 who has charge of the mill when required, 

 to start or put the wheel in motio;n, or to 

 stop it. A governor mayi also act upon 

 it, when necessary, operating by centri- 

 fugal force and motion carried to the 

 governor from the axle of the wind wheel, 

 by a band, cogs, or any other method. 

 By these means the sails are presented 

 to the wind with their sides or acting 

 faces, approaching to line with its course 

 in proportion to the degree of force with 

 which it blows. Or instead of the cogs 

 and combination of wheels, as above de- 

 scribed, the same effect may be produced 

 by one or two screws to work into the 

 cogs on the movable circle. 



The axis of the screw is placed at right 

 angles to the axis of the wind wheel, and 

 may have a fan wheel attached at each 

 end if necessary. Where two screvv 

 wheels are used they are placed at op- 

 posite parts of the periphery of the mov- 

 able circle. 



DEFINITION OF TERMS. 



Letter H. 



Hemorrhage — a flux of blood from the 

 vessels which contain it, whether pro- 

 ceeding from a rupture of the blood ves- 

 sels or any other cause. A hemorrhage 

 from the lungs is called hemoptysis; from 

 the urinary organs, henituria; from the 

 stomach, hematemesis ; from the nose, 

 epistaxis. 



Hermetical seal, among chemists, a 



method of stopping glass vessels, used in 

 chemical operations, so closely, that the 

 most subtile spirit cannot escape through 

 them. It is commonly done by heating 

 the neck of the vessel in a flame, till ready 

 to melt, and then twisting it close together 

 with a pair of pincers. Or, vessels may 

 be hermetically sealed, by stopping them 

 with a glass plug, well luted; or by cover- 

 ing the vessel with another ovum philo- 

 sophicum. 



Hexagon, in geometry, a figure of six 

 sides and angles; and if these sides and 

 angles be equal, it is called a regular 

 hexagon. 



The side of every regular hexagon, in- 

 scribed in a circle, is equal in length to 

 the radius of that circle. Hence it is 

 easy, by laying off the radius six times 

 upon the circumference, to inscribe an 

 hexagon in a circle. 



Homicide, properly so called, is the 

 killing of a man by a m,in. Of this there 

 are several species, as homicide by self- 

 defence, homicide by misadventure, jus- 

 tifiable homicide, manslaughter, chance- 

 medley, and murder. 



Hornblende, this mineral enters into 

 the composition of many mountains. It 

 is also amorphous, but frequently also 

 crystallized. The primitive form of its 

 crystals is a rhomboidal prism, the faces 

 of which are inclined at angles of 124° 34' 

 and 55^ 26', and whose bases are angles 

 of 122° 56' and 57° 4'. The most com- 

 mon variety is a six-sided prism, termi- 

 nated by trihedral or tetrahedral sum- 

 mits. 



Horse power. — A horse's power of 

 draught or carriage is thus expressed, 

 (according to professor Leslie.) If we 

 represent his force when moving at the 

 rate of 2 miles an hour by the number 

 100, his force at 3 miles per hour will be 

 81; at 4 miles 64; at 5 miles 49; at 6 

 miles 36, Desaguliers and Smeaton con- 

 sider the force of one horse equal to 5 

 men. Watt estimated one horse suflicient 

 to raise 33,000 pounds to the height of 

 one foot in a minute. 



Hydraulics. — The science which has 

 for its object the motion of fluids is called 

 hydraulics; and its immediate application 

 is to furnish us with the means of con- 

 ducting water from one situation to an- 



