126 SEC. 3. MEASUREMENT. 



434a. Eight-day Marine Chronometer. 



Parkinson fy Frodsham. 



484b. Eight- day Marine Chronometer. 



Parkinson Sf Frodsham. 



484c. Chronometer, used by Captain Parry in the year 

 1819. Parkinson fy Frodsham. 



This chronometer, used by Captain Parry in his voyage to the Polar Sea 

 in 1819, was specially compensated for extreme cold. Others of a similar 

 character were recently made for the Arctic Expedition under Captain Nares ; 

 also for Dr. Livingstone's Central African Expedition, the latter being com- 

 pensated for a higher range of temperature. 



487. Pendulum Clock for marking the time according to 

 the time system of nature, thus forming the standard of a system 

 of measurement including time and space together, with decimal 

 subdivisions. The pendulum measures space by its length, and 

 time by its period of oscillation. 



Hans Raumgartner, Basle, Switzerland. 



The pendulum has the exact length of a longitudinal uuit of natural 

 measure, that is to say, of the one hundred thousandth part of a degree, of 

 which 540 go to a meridian, and measures the natural second, or the one 

 hundred thousandth part of a mean day. 



487a. Pendulum. Professor Dr. A. Krucger, Helsingfors. 



A barometer tube of about 350 mm length is attached to the pendulum rod 

 in the plane of swinging ; a little quantity of dry air is introduced in the upper 

 part of the tube: height of the mercury column about 150 mm . The rising 

 and falling of the mercury, depending on the variations of atmospherical 

 pressure, will affect the length of the pendulum and the clock-rate. It will 

 be very easy to calculate the distance from its centre, at which the tube is to 

 be attached ; then the barometrical variation in the clock -rate will be com- 

 pensated. A pendulum of this construction has been used with success at 

 the Helsingfors Observatory since 1866. See Astrononiische Nachrichten, 

 Vol. 62, No. 1482. 



488. Clepshydral Escapement. 



Prof. W. II. Miller, M.A., F.R.S. 



By means of the fountain bottle of Berzelius, or Gay-Lussac's syphon 

 washing bottle, or any similar contrivance, a current of water is directed 

 into a capsule, from which it is transferred by a syphon to the mouth of an 

 inverted syphon partly filled with fine sand, one leg being rather more than 

 twice as long as the other. The upper end of the short leg is stopped with 

 a cork, in which is inserted a. short syphon about 0'29 inch (8 mm ) in diameter. 

 A compensated pendulum carrying near its upper end at a distance of 5-5 

 inches (140 ram ) an inverted funnel about 0-63 inches (IG" 11 --) long, 0'27 

 inches (7 mm ) wide at its base, and about 0-04 inches (l mm ) at the upper end. 

 The lower end of the upper syphon is supported at about 0-12 inch (3 mm ) 

 above the top of the funnel carried by the pendulum when at rest. A tube of 

 about 0'08 inches (2 mnl ) in diameter, and 0'4 inches (10 mra ) long, is 

 supported with its upper end about 0- 12 inches (3 mm ) below the lower end 

 of the funnel at rest. 



