114 



Level, Gravette. A form of level invented by M. Gravette. [13.] 

 Level, Hicks's. A hermetically sealed, vertical, circular level. 



[13, 21, 26, 28.] 



Level, Reflecting. A simple form using a small mirror. Some- 

 times called the Bural Level after its inventor, Col. Bural. 



[13, 17, 21, 25, 27.] 

 Level, Spirit. A glass tube almost filled with liquid, but leaving 



a small bubble to act as an index. The inside of the tube 



is ground to a definite curvature according to the desired 



sensitivity. The tube is suitably mounted to indicate level. 



[2, 3, 15, 16, 17, 19, 20, 21, 23, 24, 25, 26, 27.] 

 Level, Stride. A spirit level mounted on a frame with two legs 



shaped so as to be placed on the axis of the telescope of a 



theodolite or similar instrument. 

 Level, Surveying. A telescope mounted so that it can be readily 



placed in a truly horizontal position and used with a levelling 



staff to obtain small differences of level in surveying. [2, 



13, 15, 16, 18, 20, 21, 24, 25, 26, 27.] 

 Level, Water. An instrument to show the level by means of 



water in a trough or in upright tubes connected by a pipe. 



[21, 24, 25, 27.] 

 Level, Y. A form of surveying level in which the telescope is 



supported on two Ys. It can thus be readily reversed so 



as to eliminate errors due to the instrument not being set 



truly level. 



Levelling Rod. See Levelling Staff. [2. 3, 15, 16, 21, 24, 25, 27.] 

 Levelling Rule. A measuring rule with an attached spirit level. 



[13, 15, 24, 27.] 

 Levelling Staff. A staff, generally of telescopic construction, 



marked with divisions representing vertical heights, use, 



for surveying purposes. [2, 3, 5, 13, 15, 16, 17, 20, 21, 24, 



25, 26, 27.] 

 Levelling Stand. An instrument used in photography to support 



a glass plate in a horizontal position. 

 Lewis Thomson Calorimeter. See Calorimeter. [15, 17.] 

 Lieberkuhn. A concave metallic mirror attached to the object- 

 glass end of a microscope to concentrate light down upon 



an opaque object. [2, 3, 17, 20, 22.] 

 Life Slide. A microscopic slide with means provided to enable 



living objects to be kept alive during observation extending 



over long periods. [2, 3, 17, 26.] 

 Light-Registering Apparatus. An automatic device invented by 



Prof. Roscoe to keep a record of the amount of light that 



falls at any particular spot during small fixed intervals. 

 Lightning Arrester. A contrivance used in telegraphy for 



guarding against the passage of atmospheric electricity 



through the instruments. 

 Lightning Conductor. An appliance for protection of buildings 



against destruction or damage by lightning. Usually a 



