the Dead Escapement. 11 



planes to be different from each other, (see Note page 3, and Fig. 3, 

 Plate II., where the same effect is more visibly shewn,) and in the 

 second, and this is a most material objection, would entirely pre- 

 vent the application of the rule about to be shewn for determining 

 the distance between the center of the wheel and the center of the 

 pallets. 



Ferdinand Berthoud, in his last and great work L'Histoire de 

 la Mesiire die Terns, 4to., Paris, 1802, in vol. 2, page 26, speaking 

 of Graham's escapement, which he does very briefly, thus ex- 

 presses himself, quoting M. Thiout, " La regie que j'ai trouve (dit 

 M. Thiout,) et qui me paroit assez convenable est d'eloigner le cen- 

 tre de l'ancre de la circonference de la roue d'un diametre du 

 rochet comme la figure le represente." This is translated at page 

 2, under the head of M. Thiout. 



In Dr. Rees' Cyclopcedia, 4to edition, (Vol. XIII. Part II..) under 

 the head of " Escapement," among other escapements described is 

 the " Anchor Escapement, by Clement, or Dr. Hook," and " Gra- 

 ham's dead beat." In the first it is inferred that the distance be- 

 tween the centers of the pallets and scape wheel, regulates the arc 

 of vibration of the pendulum. This, as has been before observed, 

 is not the case ; (see note, page 3,) and in both, that the dis- 

 tance " is determined by tangent lines." This cannot be better 

 explained than by the following quotation from the explanation of 

 " Graham's dead beat," which applies equally to the principle 

 upon which the anchor escapement is constructed. " In this con- 

 struction, as in the preceding one, the distance of the centers of 

 motion a, b, (Fig. 4, Plate XXXII., Rees' Cyclopaedia,) is deter 

 mined by the tangent lines meeting the radii at the points of 

 the acting teeth ; when the distance is an exact diameter of the 

 escapement wheel, we find that the pallets take in just ten teeth 

 out of thirty, which is the case in the figure before us ; but when 

 twelve teeth are taken in, the center of the anchor's motion falls 

 at h, just a diameter and a half from the center of the wheel." 

 This is not correct, for it will be found by reference to Fig. 4, Plate 

 IV., that when the pallets take in ten teeth, the center of mo- 

 tion of the pallets determined by " tangent lines," is at a distance 



