134 



Parallactic Instrument. An instrument invented by Ptolemy 

 for determining the moon's parallax. 



Parallel Chart Dividers. A fine pointed divider (q.v.) for setting 

 off parallel lines and accurately marking a ship's position 

 on the chart. [2, 13, 15, 16, 17.] 



Parallel Circular Plates. Optically worked parallel glass plates. 

 [10, 13, 15, 20, 21.] 



Parallel-Compressor. A means for holding or compressing an 

 object under the microscope. It consists of two frames, 

 each carrying a thin glass, and mechanism for bringing the 

 glasses together while keeping them parallel. [2, 3, 20.] 



Parallel Dividers. For the use of draughtsmen. See Parallel 

 Chart Dividers. [2, 13, 15, 17.] 



Parallel Rule, Rolling. A single bar fitted with two toothed 

 rollers of equal diameter running on spindles, for the drawing 

 of parallel lines. See also Rolling Instrument. [2, 5, 6, 13, 

 15, 16, 17, 20, 21, 24, 25, 26, 27, 28.] 



Parallel-Ruler. A draughtsman's instrument for drawing 

 parallel lines. [2, 5, 13, 15, 16, 17, 20, 21, 24, 25, 26, 27, 28.] 



Paralleloscope. An instrument for using gunsights in a confined 

 situation. [3, 20] 



Paschen Galvanometer. See Galvanometer. [4.] 



Paterson's Lamp-Rotator. See Lamp-Rotator. 



Peake's Patent Control Board. An electrical device for use 

 with the thermo-electric pyrometer, enabling the scale of 

 an indicator or recorder to commence at any desired 

 temperature, thus allowing of a more open scale over the 

 working range of temperature. [4.] 



Pedometer. An instrument to count the steps by registering the 

 rise and fall of the body. A pace measurer. It is usually 

 in the form of a watch. [5, 6, 9, 13, 15, 16, 17, 20, 21, 24, 

 25, 26, 27.] 



Peirameter or Pirameter. An instrument to indicate the amount 

 of resistance offered by the surface of roads. 



Pelorus or Dumb Plate. A dumb compass card (without 

 magnetic needles), or azimuth dial, supported in gimbals 

 and fitted with sight vanes for telling or reading off a 

 bearing. [13, 15, 16.] 



Pelvimeter. An instrument to measure the diameter of the 

 pelvis. 



Pendant Clinometer. A hanging clinometer. See Clinometer. 



Pendulum, Ballistic, Hicks's. An instrument for comparing 

 moments and investigating the laws of inelastic impact, 

 consisting of a wooden framework with three cross-pieces 

 screwed to the top, from which are suspended, by strings, 

 two light wooden platforms, carrying weights and with 

 pointers attached, by means of which the distance apart of 

 the platforms may be ascertained upon a divided scale 

 below. [19.] 



