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46 THe MarRINeE REVIEW Apparatus for Recording the Rolling and Pitching While engaged in determining the gravity constant at sea, Prof. O. Hecker, of Potsdam, an acknowledged authority in this field, was troubled with the difficulty of taking accurate barometric readings with the usual rolling even of a steady ship. The outcome of his experiments has been a very simple apparatus for register- ing the rolling and pitching of ships, which he describes in a recent issue of the Zeitschrift fur Instrumenten- kunde. The substance given herewith was condensed by Engineering, London. When a barometer is inclined to the vertical by the angle a, the true read- ing of the barometer will be B= Bi cos a, where B, is the apparent read- ing. As long as.a is measured in minutes, the difference between the true and the apparent readings may be neglected. But for a = 1 deg. of arc the difference would already amount to 0.16 millimeter of mercury, and for a = 2-deg., to 0.46 millimeter. It is, therefore, necessary to measure the inclination of the ship, so as to make the necessary barometer correction. If a pendulum is suspended on board ship in such a way that it can swing only transversely, the pendulum will be set into oscillation by the rolling of the ship, and its motion will be the result both of the change of inclina- tion and of the horizontal displace- ment of the point of suspension. The object of Hecker's device, now under notice, is to arrange the pendulum so as to minimize the horizontal dis- placement. The pendulum will then practically indicate the momentary inclination of the ship, which has to be ascertained. A formula for the amplitude of the oscillation wh'ch a pendulum describes under the influ- ence of the horizontal displacement of its point of suspension was com- municated by Wiechert to the first International Seismological Confer- ence meeting at Strasberg, in 1902. Applying that formula, Professor Hecker demonstrates that the object stated--the diminution of the _ hori- zontal displacement--can be secured in various ways, best by making the ratio of the periods of rolling Ti to the natural periods of the pendulum Ts Lf ks, as latee. as «possible; in other words, by making the period of the pendulum very small. The pen- dulum should hence be short, but suf- ficiently heavy, of course, to over- come friction. Fig. 1 illustrates the apparatus of Ships. which Professor Hecker designed for this purpose. There are two pendu- lums, one for registering the rolling, the other for the pitching. The pen- dulums are stout, heavy discs, pivoted near their circumference. The length of the corresponding mathematical pendulum can be deduced from the formula :-- "On rdrt oe | fer = 37, 0 where ry is the radius of the disc. If r = 2 centimetres, the length of the mathematical pendulum would be 3 centimetres, and its period 0.18 sec- ond. The style attached to the pen- dulum has a length of 114 centi- metres, and with these dimensions an inclination of the ship by 0.5 deg. would produce a motion of the style through 1 millimetre. Hecker found that the large ships on which he ex- perimented had rolling periods rang- ing from about 10 to 30 seconds; we shall revert to this point again, how- ever. According to Wiechert's for- mula, the just-described apparatus would reduce the horizontal displace. ment of the point of suspension for the two periods mentioned to 0.0049 or 0.0005 of its true amount. The effect of that horizontal displacement can hence be neglected, provided the pendulum be suitably suspended. The amount of the horizontal displacement is not the same for all parts of the ship; the pendulum should be sys. pended near the longitudinal axis, -about which the ship is o-cillating, where the displacement is smallest, In the actual apparatus the discs are made of brass, 40 millimetres ip diameter and 16 millimetres in thick- ness; the styles, of aluminum, resem- ble the styles of barographs. The endless paper belt, on which the rec- ords are inscribed, is stretched over two cylinders, one of which is turned by clockwork at the rate of 12 milli- metres per minute. In the improved form of apparatus which the optical workshops of R. Fuess, of Steglitz, Berlin, are constructing, the paper is continuous and the motion of the pendulum is damped by a liquid. The upper pendulum records the rolling; its axis is parallel to the longitudinal axis of the ship. The near FIG, Fig. 2."sonoma" 6000 REG. TONS 1. a MANCHURIA™ 13700 REG. TONS Fig. 2. ee Ne mtcrr Fig. 4." PRINCESS3-ALICE "11000 REG.TONS RINALDI NAPPI DLA PNA PN En (662.8) : mon Ulli Fig.5.' 'TANGLIN" 1200 REG TONS eye]