130 SEC. 3. MEASUREMENT. 



but likewise the whole pendulum is directly controlled in the pyrometer. The 

 pyrometer employed is of quite a novel construction ; the observation takes 

 place in a liquid, without contact, under two micrometer microscopes. As 

 the observation through the microscope requires water of perfectly equable 

 temperature, the uniform^ of its temperature is ensured ; the bars likewise 

 must be quite homogeneous, as otherwise a bending of them will take place 

 by a change of the temperature, whereby the terminal ends will move out of 

 the range of vision. With regard to compound pendulums, the centre of 

 gravity is to be found by means of a balance the point of flexion of the spring 

 of which is known to the exhibitor, and then the point of oscillation by cal- 

 culation ; in a quite homogeneous and uniformly strong spring it is exactly in 

 the centre. By means of a bar, which is adjusted exactly to the length of the 

 pendulum,* the point of oscillation can be exactly fixed in the pyrometer, and 

 the whole pendulum examined with regard to extension and stability. The 

 working of the clock affords a check upon the accuracy of the measurement ; 

 if no error be made, the pendulum thus adjusted and fitted to a clock will 

 exactly vibrate seconds. 



521. Model Escapement. F. Denckcr, Hamburg. 



An anchor escapement, enlarged tenfold, with an impulse derived from 

 the chronometer and acting like the same from fork upon balance. This 

 requires no oil. The straight lines of the fork and the release stone 

 render a quite exact execution possible, and consequently an effect which 

 almost equals the direct impulse from wheel upon balance, without detracting 

 from the great insensibility of the anchor escapement. The lifting which 

 it is desired to give to the balance in this case is determined only by tbe 

 length of the fork, independent of the length of the lever. Arranged for 

 quarter seconds, it will be very useful for determining the time on journeys 

 and on sea. The last seconds are regulated by a curb, permitting only 

 little motion, but being securely guided by means of a screw. The last regu- 

 lation by the balance screws always disturbs the equilibrium of the balance, 

 and effects thereby a doubling of the errors at the change of the position. 

 The flat spiral spring has an inner and an external curve. 



522. Gold Watch. F. Dencker, Hamburg. 



The pocket watch has been executed exactly according to this model in 

 the exhibitor's establishment at Geneva. It is provided with a flat spiral 

 spring hardened in fire according to his invention. Up to the present time 

 no flat spiral springs hardened in fire are employed, as far as the exhibitor 

 knows. 



523. Watch with spindle without spiral spring ; constructed 

 in the East in the first half of last century, indicating month, day, 

 and hour in Arabic figures. (JRemariable for its age and origin.) 

 Property of H.H. Prince Pless, Fiirstenstein. 



The Breslau Committee. 



V 



523a. Watch, thickness of a crown piece, made for the late 

 Sir C. Wheatstone bv Mr. A. Stroh. 



* The extension of the parts to be employed being known, a pendulum can be deter- 

 mined by calculations which swings in exactly one second. 



