103 



Hematachimeter. A form of apparatus for measuring the 

 velocity of the blood. 



Hemorheumoscope. An instrument for observing the flow of 

 blood in a vein. 



Herschellian Telescope. See Telescope. 



Hicks 's Ballistic Pendulum. See Pendulum. 



Hicks's Level. See Level. [13, 21, 26, 28.] 



Hicks's Marine Clinometer. For indicating the heel of the ship. 

 [13, 15, 16, 21, 28.] 



H.M. Gauge. 



Hobson's Pyrometer. See Pyrometer. 



Hodometer. See Odometer. 



Hoffman Head. A special form of tripod head for surveying 

 instruments. [17, 18, 24, 25, 27.] 



Hole Gauge. See Gauge. 



Holometer. An instrument for making all kinds of angular 

 measurements. See Pantometer. 



Holophote. A lamp with lenses or reflectors to collect the rays 

 of light and throw them in a given direction. 



Hooke's Cyclograph. See Cyclograph. 



Horizon Glass. The silvered mirror or speculum attached to the 

 frame of a quadrant or sextant, the upper half of which is 

 left clear, enabling the horizon to be seen directly through 

 it. The image of the sun or star is seen by reflection from 

 the index mirror of the sextant in the lower or silvered part. 

 The clear or upper half of the horizon is sometimes removed 

 when the sextant is only to be used for shore angle work. 

 [3, 6, 13, 15, 16, 17, 18, 24, 26.] 



Horizontal Dial. A dial having its plane set parallel to the 

 horizon and fitted with a gnomon or sight which can be 

 revolved for observing horizontal angles. [13, 15, 16, 25, 28.] 



Horn Centre. Used in the drawing office ; to save drawings 

 from being marked by the points of the compasses. [2, 5, 6, 

 13, 15, 17, 21, 24, 26, 27.] 



Horologe. A sundial or mechanical contrivance for showing 

 the time. [20, 27.] 



Horometer. An instrument for measuring time, as a clepsydra, 

 clock, dial, or watch. 



Horoscope. An optical instrument for observing the time as 

 indicated by the position of the stars and planets. 



Horse-Power Computing Scale, Hudson's. A simple rule of the 

 sliding class for calculating at a glance the horse-power from 

 the proportions of a steam-engine. [5, 15, 21, 24.] 



Hoskold's Transit Theodolite. See Theodolite. [13, 25, 27.] 



Hourglass. An instrument for measuring time, especially the 

 interval of an hour. It consists of a glass vessel having 

 two compartments, from the uppermost of which a quan- 

 tity of sand, water, or meicury occupies an hour in running 

 through a small aperture in the lower. See also Log-glass. 

 [2, 6, 13, 15, 16, 17, 21, 28.] 



