40 REPORT — 1869. 



Admiral Paris has invented a self-recording instrument for the purjiosc 

 of measuring- both the height and form of waves. A description of this will 

 he found in the Trans. I. N. A. vol. viii. 1867, p. 279. It is unfor- 

 tunately a differential instrument, Avithout any means of getting a good 

 datum line. It appears to he much better adapted for getting approximate 

 profiles of complex waves than for obtaining accurate measurements of 

 simple ones. 



Observations on the lengths of waves present much less diiRculty: a 

 float, sunk so as not to catch the wind (such as a bottle), and observed from 

 a considerable height, wiU give the periodic time with a fair degree of ac- 

 curacy, and the length may be inferred from the period. 



General observations upon waves* are not in point. The object in the- 

 present case is to ascertain what the particular waves are in which the 

 ship's rolling is being observed. 



Measurement of Boiling. 



It is very well known that a pendulum at sea docs not give a vertical 

 line, but a direction due to the joint cfiect of gravity, of its own free oscil- 

 lation, and of the forced oscillation due to the motion of its point of sus- 

 pension. A suspended clinometer is thus perfectly useless for this purpose. 

 Uaromctcrs, cuddy-lamps, and chandeliers generally oscillate through larger 

 angles than the ship. 



Mr. Froude (Trans. I. N. A. for 1SG2, p. 41) suggests watching the 

 rattlins of the rigging come down to the horizon, as a ready and fairly 

 correct way of measuiing the roll. The motion of the mast-heads rcla- 

 livcly to the stars may be used in the same waj'. 



M. Normand, jun., of Havre, has invented a very ingenious clinometer 

 suspended on gymbals, like a chronometer, in such a way as to be as little 

 as possible influenced bj' the ship's motion f. We do not consider that any 

 instrument depencUng upon gravitation is to be relied upon at sea, and 

 we have been informed that M. Normand himself is not quite satisfied with 

 his instrument. 



Apart from observations depending on the stars, or actual sea-horizon, 

 the only instrument that can be relied ujion as giving an invariable plane is 

 of the gyroscope class. A modification of Foucault's gyroscope was tried in 

 the North Sea in 1859, by Professor C. Piazzi Smyth, who gave an account 

 of the instrument and its performance in the Trans. I. N. A. for 1863, 

 p. 118. 



An instrument upon the same rotatory principle, but self-recording, has 

 been invented by Admiral Paris, Hydrographer of the French Imperial 

 Navy. It consists of a spinning top, with its point of support above its 

 centre of gravity. It spins in an agate cup, and the top of the spindle 

 carries a camel's-hair pencil which marks a paper band, driven by clock- 

 work, and passing through bent guides so as to keep close to the pencil. 

 It is described, and some of its curves copied, in the Trans. I. N. A. 

 vol. viii. for 1867. 



What these instruments really give is the deviation from an undeter- 

 mined direction. They therefore give the time of rolling or pitching, and of 

 any intermediate oscillation of a periodic character, and the amplitude of 



* Although very desirable for other reasons. 

 t See Trans. I. N. A. for 1866, p. 187. 



