100 SEC. 3. MEASUREMENT. 



This timekeeper is thus spoken of in Cook's Voyage to the Pacific, 1776, 

 Vol. I., p. 4 : "I had likewise in my possession the same watch or time- 

 " keeper which I had in my last voyage, and which had performed its part 

 " so well. It was a copy of Mr. Harrison's, constructed by Mr. Kendall." 



This watch was taken out again by Captain Bligh, 1787, and when the 

 crew of the " Bounty " mutinied it was carried by the mutineers to Pitcairn's 

 Island. In 1808 it was sold by Adams to an American, Mr. Mayo Fletcher, 

 who sold it in Chili, and in 1840 it was purchased for fifty guineas by Sir 

 Thomas Herbert. It was repaired and rated at Valparaiso, and taken by Sir 

 Thomas to China, and brought home in the " Blenheim" in 1843, having kept 

 a fair rate with the other chronometers for the space of three years. 



Presented to the institution by Admiral Sir Thomas Herbert, K.C.B. 



485. Universal Dial, in use about 160 years ago. 



The Royal United Service Institution. 



Presented to the United Service Museum in 1838, by His Royal Highness 

 the Duke of Sussex. 



486. Month Equation Clock, with double pendulum and 

 dead-beat escapement by Quire, showing minutes and seconds both 

 sidereal and mean time, also sun fast or slow, and containing an 

 annual almanack, mentioned in Cooke & Maule's account of 

 Greenwich Hospital in 1789. Royal Naval Museum, Greenwich. 



487. Pendulum Clock for marking the time according to 

 the time system of nature. 



Hans Baumgartner, Basle, Switzerland. 



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

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

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

 hundred thousandth part of a mean daj r . 



487 a. Pendulum. Professor Dr. A. Kreuzer. 



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 15 O mm . The rising 

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

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

 be very easy to calculate the distance from centrum, 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 Etchingforr Observatory since 1866. See for theory: Astronomische 

 Nachrichten, Vol. 62, No. 1482. 



488. Clepshydral Escapement. 



W. H. 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 '29 inch (8 miu ) in diameter. 

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



