104 SEC. 3. MEASUREMENT. 



structed repose pendulum, executed with sufficient stability. Not only is the 

 expansion coefficient of the separate bars exactly determined in the pyrometer, 

 but likewise the whole pendulum is directly controlled, as regards length 

 and extension, 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. Accuracy : 1 scale division = t ^ milli- 

 meters. As the observation through the microscope requires perfectly clear 

 water, the uniformity 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; in a quite homogeneous and uniformly 

 strong balance it is exactly in the centre. By means of a bar the centre of 

 gravity is indicated on the length of the pendulum,* and the whole pendulum 

 is controlled in the pyrometer as to temperature and stability. 



521. Model Escapement. F. Dencker, Hamburg. 



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

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

 same moves likewise without 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. 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 

 regulation by the 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 exactly executed 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 are ever hardened in fire. 



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. (Remarkable for its age and origin.) 

 Property of H.H. Prince Pless, Fiirstenstein. 



Committee of Breslau. 



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

 Sir C. Wheatstone by 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. 



