sr I KNCK. 







1criptinn 

 f UieuM. 

 k.-e' chro- 

 wojrapli. 



Description 

 t' Irriebel'a 

 portable 

 night clock. 

 PLATE 

 ccccixxxv, 

 7, 8. 



Description 

 f Lenor- 

 mand's new 

 chronome- 

 ter. 



Figs. 9, 10, 

 11. 



In order to use tins instrument the minute* and tens 

 of seconds are first observed on the dial plate KF, a few 

 seconds before the star reaches the wires, then by rais- 

 ing the eye to the field of the telescope, the shortest 

 needle n points out the units of seconds which re to 

 be added. The eye of the observer must now be fixed 

 aolely upon the star which is about to pass behind the 

 first wire, and he reckons fractional parts of the seconds 

 by observing laterally and indirectly the passage of 

 the disc m over the divisions from to lo. 



M. Breguet has not yet published any account of the 

 interior arrangements of the chronometer. 



2. Description of Rieussec's Chronograph. 

 This piece of watch-work was invented by M. 

 Rioussec in 1821, and has been grc-atly improved by 

 M. Breguet. The object of it is to record on the dial 

 plate the fractions of seconds at any instant of time, so 

 that it enables us to determine with great accuracy in 

 seconds and fractions of a second the interval elapsed 

 between any two instants. The needle is supplied 

 with as much of a prepared black colour as will t>erve 

 for fifty exoeriments. The instant that we press down 

 a button, the needle deposits a black point on the dial 

 plate during five minutes, so that these points can- 

 not be confounded with one another. This instru- 

 ment, which is singularly accumte, has a dial plate 

 with second and minute hands. In M. Rieussec's in- 

 strument printer's ink is used far marking the points, 

 and the instantaneous contact of the point has no in- 

 fluence on the motion of the dial, which is moveable. 

 In Breguet's, the dial seems to be fixed. 



3 Description of Griebel's Portable Night Clock. 



This clock, constructed by M. Griebel of Paris, 

 is represented in Plate CCCCLXXXV. Fig. 7. and 

 Fig. 8. the former showing it in perspective, and the 

 latter in section. A is the globe which contains the 

 clock movement and the lamp B. The dial-plate C 

 has a rim of a round glass with the hours painted up- 

 on it between E and C ; EE is a plate in the centre 

 of the ground glass ring to which the movement is 

 fixed, and F is a globe to protect the wheel-work from 

 dust. The rays of light BG, BG issuing from the 

 lamp B, illuminate the rim EC of the dial on which 

 the hours and minutes ace painted. 



It would, we think, be an improvement on this 

 clock to place a mirror between GG, to intercept all 

 the rays that do not fall upon the rim of ground glass, 

 which by means of another mirror behind B, would 

 throw some additional scattered light on the rim itself, 

 while it v. - ould protect the wheel-work from the direct 

 radiation of the lamp. See Dr. Brewster's Edinburgh 

 Journal of Science, vol. iii. p. 346. 



4. Description <f Lenormand's New Chronometer. 



This very singular piece of mechanism, which ex- 

 cited much interest at the expositions of French in- 

 dustry in 1819 and 1823, is represented in Plate 

 CCCCLXXXV. Figs. 9, 10, 11. The principle of 

 this chronometer consists in the continual displace- 

 ment of the centre of gravity of the arm of a lever. 

 This lever has the form of an arrow AB, Fig. 9. 

 which is capable of moving round a horizontal axis 

 O, fixed in the middle of a dial-plate divided into 

 twelve hours. The two arms AO, BO are unequal, 

 and at the end B is fixed a round box. If we place in 

 the box a small weight, which has the power of mov- 

 ing round the interior circumference of the box, ami 



VOL. XVII. PART II. 



if it M placed as at H, the arrow will remain in the >"<*. 

 portion AB, and point to IX*. It the email . 

 M pltced at at I>, so at to be at the greatest pouible 

 distance from the centre (), the arrow will point to V *^Y**' 

 XI I h , and KO on at the other Quarter*, a* at k. and F 

 in Fig. 10. In like manner, intermediate portions of 

 the little weight will cause the arrow to point to in- 

 termediate hours. If we now could fix in the box a 

 piece of wheel-work to displace this weight in a re- 

 gular manner, so as to describe the circumference of 

 the box in twelve hour*, the arrow AB would revolve 

 in twelve hours, and would point them out on the 

 dial-plate like the hand of a clock. If the wheel-work 

 should carry the weight round the box hi an hour, the 

 arrow would mark minutes on the dial. The additional 

 \vtii>ht which we have introduced for the purpose of 

 explaining the principle of the machine, is not actual- 

 ly ue<i. It exists naturally in every watch, as the 

 centre of gravity of every watch is at a distance from 

 its centre of form, on account of the weight of the 

 main-spring box and fusee. We require, therefore, 

 only to place a watch in the box B, Fig. 10. in such a 

 manner, that it cannot go without communicating ita 

 motion to the arrow AB. This may be done in two 

 ways, 1st, The axle of the central wheel, at the place 

 where it comes out of the plate in which it moves, 

 curries a square which is laid hold of by one of the 

 two cross pieces between which the watch is carried, 

 which cross pieces are fixed to the box. The other 

 end of the axle, which is round, moves in a hole per- 

 forated in the opposite cross piece. This method, 

 though the most simple, is not always so convenient 

 as the following : 2d, On one of the cross pieces above 

 mentioned is fixed a wheel O, Fig. 11. which cannot 

 turn round. Above the plate of the watch passes the 

 axle of a wheel, on which is fixed a pinion II, which 

 works in the wheel O. The wheel-work actuated by 

 the spring not being able to turn the wheel O, turns 

 quite round it, and, consequently, carries the centre 

 of gravity of the watch quite round the interior cir- 

 cumference of the box B, Fig. 9- and this changes at 

 every instant, and in a regular manner, the centre of 

 gravity of the arrow. If the axle of the wheel, which 

 carries the pinion R, turns round in one hour, and if we 

 wish AB to revolve in twelve hours, then R must hare 

 eight teeth, and O 9<3; or R 10, and O 120. If AB 

 is to revolve in one hour, then R and O must have the 

 same number of teeth. See Baron Ferussac's Bull, dtt 

 Sc. Technol, Jan. 1825, p. 12. or Edinburgh Journal of 

 Science, vol. iii. p. 848. 



5. Breguel's Chronometer trilh Double Seconds. 



This little contrivance, which is constructed for 

 sale by M. Breguet, has sometimes a dial-plate with ch 

 two second hands, and sometimes two dial-plates and * 

 two second hands. In order to determine any interval * 

 of time, the observer, at the commencement of the 

 observation, presses a button, and stops one of the 

 needles, and when the observation is concluded, he 

 again sets the same hand agoing. The difference be- 

 tween the two second hands snows the interval re- 

 quired, an account being kept of the minutes if the 

 interval exceeds (JO seconds. 



6. Bregvet's Dottble Sympathetic Chronometer. 

 This curious time-piece consists of two independent 



watch movements in the satire box, and without any srrop*rheiic 

 mechanical communication, hiving each their separate 

 4 o 



