HOROLOGY. 



takes place after the drop which drives 

 the pallets back, and causes the index 

 also to recede through a small arc : this 

 has been distinguished by the name of a 

 recoil. Other considerable objections, 

 besides that of the continued action of 

 the maintaining power, have been made 

 against escapements with a recoil ; but it 

 would lead us too far into the minute de- 

 partments of this subject to discuss them. 

 The escapement of Graham, and all such 

 i as have no recoil, have been called dead 

 I beat escapements, because the index for 

 ! seconds falls directly through its arc, and 

 I remains motionless on the line of division 

 I till the next vibration. It may be observ- 

 i ed, that the maintaining power in Gra- 

 ! ham's escapement may be applied during 

 a small portion only of the vibration ; 

 and that an increase of the maintaining 

 j)ower tends to enlarge the arc of vibra- 

 tion, but scarcely interferes with its velo- 

 city. 



The effect of the escapement which has 

 been termed horizontal, because the last 

 wheel in watches of this construction has 

 its plane parallel to the rest of the sys- 

 tem, is similar to that of the dead beat 

 escapement of Graham. In fig. 3, the ho- 

 rizontal wheel is seen with twelve teeth, 

 upon each of which is fixed a small wedge 

 supported above the plane of the wheel, 

 as may be seen at the letters A and B. On 

 the verge of the balance there is fixed 

 part of a hollow cylinder of steel, or other 

 hard material, the imaginary axis of which 

 passes through the pivots of the verge. 

 C. represents this cylindrical piece, into 

 which the wedge D. may be supposed to 

 have fallen. While tiie vibration causes 

 the cylindrical piece to revolve in the di- 

 rection which carries its anterior edge to- 

 wards the axis of the wheel, the point of 

 the wedge will merely rub the internal 

 surface, and no otherwise affect the vibra- 

 tion of the balance than by retarding its 

 motion. But when the return of the vi- 

 bration clears the cylinder of the point of 

 the wedge D, the wheel will advance, 

 and the slope surface of the wedge, act- 

 ing against the edge of the cylinder, will 

 assist the vibration of the balance. When 

 the edge of the cylinder- arrives at the 

 outer point of the wedge D, its posterior 

 edge must arrive at the position denoted 

 by the dotted lines of continuation ; im- 

 mediately after which the wedge or tooth 

 E will arrive at the position e, and rest on 

 the outer surface of the cylinder, where 

 it will produce no other effect than that 

 of retardation from friction, as was re- 

 marked with regard to the wedge D, un- 

 til the course of the vibration shaft bring 



the posterior edge of the cylinder clear of 

 the point of the wedge. In this last si- 

 tuation the wedge will acton the edge of 

 the cylinder, and assist the vibration, as in 

 the former case, until that edge shall ar- 

 rive at the outer or posterior point of the 

 wedge; immediately after "which the 

 leading point will tall on the inner sur- 

 face of the cylinder in the first position, 

 as was shewn in the wedge D. 



Time-pieces, with a pendulum regula- 

 tor, are certainly the most perfect, when 

 they are kept in a fixed situation ; and, 

 for that reason, these are the only sort 

 used in astronomical observatories. But 

 external motion is so contrary to the re- 

 gularity of their performance, that no sea 

 chronometer has been since attempted to 

 be constructed upon that principle. The 

 balance regulator remained, as affording 

 the only method by which the desired 

 uniformity might be obtained in portable 

 machines ; and the great improvement 

 made in that regulator, by the addition of 

 a spiral spring, may be considered as one 

 principal cause of the perfection which 

 has been since attained in them. The first 

 invention of attaching a spring, to give to 

 the balance, by its elasticity, a power 

 which renders the action of this sort of 

 regulator similar to that of gravity in the 

 pendulum, is undoubtedly due to Dr. 

 Hooke, though it is not so clear whether 

 he ever applied it in the shape of a spiral, 

 as has been so long practised since. F. 

 Berthoud, in his " Histoire de la Mesure 

 du Temps," (vol. i. pp. 134 to 141,) gives 

 a body of extracts from several works re- 

 lative to this subject j and concludes, that 

 Dr. Hooke only applied a straight spring 

 to the balance, and that M. Huygens im- 

 proved upon that idea, and contrived the 

 spiral spring, which is more favourable to 

 the vibrations of the balance. M. Huy- 

 gens, indeed, applied in France a balance 

 spring, the account of which has been 

 published in the Philosophical Transac- 

 tions for 1675, No. 112 ; but Dr. Hooke, 

 in the Postscript to his Description of He- 

 lioscopes, asserts, that the hint was taken 

 from the experiments he had made in 

 1664, in Gresham College, where he ex- 

 plained above twenty several ways, by 

 which springs might be applied to do the 

 same thing. 



In relating the progress of time-piece 

 making, we must not omit mentioning the 

 use of precious stones, particularly rubies, 

 to form the holes in which the pivots of 

 the wheels turn, and the pallets upon 

 which the action of the teeth is exercis- 

 ed. These jewels, by the high polish 

 given to them, reduce the quantity of 



