Performance of Some Timekeejiers. 177 



than would result from a slight deviation from the isochronal 

 length of the spring ; and here it may be remarked that the 

 usual way of making this alteration by means of a lever, 

 containing two curb pins, which works radially round the 

 spring, is by no means delicate enough. Some of the 

 Waltham watches have very beautiful arrangements for this 

 purpose, so that very minute alterations may be easily 

 effected. Yet, strange to say, I find only their watches in 

 hunting cases so provided ; the similar grades of open face 

 watches have the ordinary radial arm. The usual form of 

 balance spring for watches is the well known fiat spiral. In 

 marine chronometers the heliacal spring is used, and for 

 lever watches of the best class, especially those that have 

 large arcs of vibration, amounting occasionally to 540 degs., 

 a flat spring, with the outer end bent over and fixed not far 

 from the centre coil, is preferred. Such a spring is known 

 among the English as a Breguet, or overcoil, spring. The 

 French call it spiral coude. Many other forms of spiings 

 are sometimes found, but, judging from the results of the 

 severe timing contests that take place among the Swiss 

 manufacturers, no one form of spring is certain of proving 

 itself superior to another. From what has been said above 

 it will be seen that the selection of a proper spring for 

 a watch demands great care, for unless the spring be 

 isochronal great variations of rate would take place during 

 the day, as the arc of vibration diminished with the 

 uncoiling of the mainspring. This diminution, according to 

 the observations of M. Phillippe, amounts to from 65 to 

 112 degrees. The English have endeavoured to evade this 

 difficulty by the use of a fusee to equalise the force of the 

 mainspring. This, however, considerably complicates the 

 mechanism. It also renders rather difficult the application 

 of the kejdess mechanism, which is fast superseding the old 

 style of winding, and worthily so, for, independently of its 

 great convenience, the winding is done in a plane at right 

 angles to that of the watch, so that there is no fear of 

 disturbing the arc of vibration, as is done by those careless 

 persons who, when they wind with a key, turn the watch as 

 much, or even more, than the key itself. Keyless watches 

 also keep clean longer than others. It has been remarked 

 that the introduction of the keyless watch will be the death 

 blow to the fusee. Strictly speaking every mainspring 

 should have its own proper fusee, a point that was generally 

 attended to in the best class of old verge watches; but 



o 



