486 



NA TURE 



[_Sept. 2 2, 1887 



each station the watchman had to visit, and by pulling a 

 string or handle he was enabled to leave record of his 

 presence. Now, either he carries the clock (or large 

 watch) with him, or else it is fixed at a central station, 

 and is operated upon by electricity. In the first case 

 there is a revolving paper dial inside the clock, and by 

 placing the clock within specially arranged orifices at the 



who made it. At one large lunatic asylum the system is 

 so perfect that the night superintendent, sitting in his 

 own room, can follow the movements and whereabouts 

 of all his men. Clocks have also been designed for 

 registering the gross aggregate or integral of daily tem- 

 peratures or barometric pressures. In the former case a 

 watch is used, and has a balance compensated the wrong 

 way, so that the effects of changes of temperature are 

 magnified. In the latter case a barometer is used as the 

 pendulum. 



Until three years ago there was no public institution in 

 Great Britain where a serviceable authentic trial of the 

 performance of a watch under varying conditions as 

 regards temperature and changes of position could be 

 obtained. At that date, however, under the auspices of 

 the Royal Society, a department of the Kew Observatory 

 was established for the purpose. It satisfied a want which 

 had long been felt, and provided with every requisite for 



Fig. 10. — Brocot's Perpetual Calendar. 



different stations he has to visit, he is enabled to get 

 printed off upon the paper dial a mark or letter showing 

 the time at which he was at the station. In the latter 

 case the clock is provided with a large drum or cylinder, 

 and wires lead to it from the different stations ; and when 

 a button at any station is touched, a mark follows upon 

 the cylinder, indicating the where and when of the person 



Fig. II. — Dial of Brocot's Perpetual Calendar. 



timing both in temperatures and positions, a considerable 

 and increasing number of watches are regularly sent there 

 for the purpose of obtaining its certificates. In Class A 

 (the first class) merit-marks are awarded in addition to 

 the certificates, in the following proportions ; 40 for a 

 complete absence of variation of daily rate, 40 for abso- 

 lute freedom from change of rate with change of position, 

 and 20 for perfect compensation for effects of tem- 

 perature. 



The subject of the appHcation of the balance-spring, 

 and the process of timing, which is subsequent, must be 



Fig. 12. — Diverse forms to which balance-springs are fashioned. 



reckoned beyond the scope of the present article. But 

 we may briefly allude to the fact that the causes which 

 operate upon a watch to make it keep different times in 

 different positions are generally three. For instance, the 

 balance may be out of poise, the balance-spring may not 

 be isochronous, and the action of the escapement 

 generally is irregular in different positions. Putting the 



balance in poise is done roughly in a poising tool ; the 

 finer adjustment follows the results of trials when the 

 watch is kept going in different positions. Isochronism 

 is more important and more difficult of attainment. 

 Without isochronism a watch might keep tolerably near 

 time when placed successively 12, 3, 6, or 9 upwards, and 

 still possess a very wide error between all these and the 



