66o THE POPULAR SCIENCE MONTHLY. 



on such matters ; but he is a very exceptional man if he has any con- 

 siderable knowledge of the principles underlying the construction of 

 the most common chronometers, so far as they employ principles not 

 found in common clocks. In illustration of this ignorance of the sub- 

 ject, even among workmen who are thoroughly competent to treat all 

 the disorders of time-pieces properly, and that to the degree of con- 

 structing broken or missing parts, or of mending fractures so nicely as 

 to leave no trace of a break, the following instances may be given : 



The clock most commonly used by the watch-makers as a " regu- 

 lator" is one with what is called a "gridiron" pendulum. This con- 

 sists of nine brass and steel rods, side by side, with their couplings 

 so arranged that, in the changes of temperature, the variation of the 

 brass counteracts that of the steel. Now, it is the fact that a large 

 per cent of these pendulums are simply false "gridirons," while a 

 very small per cent of the watch-makers are able to tell the difference. 

 One might suppose that the running of* the clock would reveal this 

 at once. But it should be remembered that the variations of a clock 

 on account of temperature are very slight. An abrupt change of ten 

 degrees maintained through twenty-four hours will cause a seconds 

 pendulum to vary but a little over two seconds. Bearing in mind, 

 then, that a pendulum may be timed to a mean temperature, and that 

 thus the variations would tend to equalize each other ; that, if the 

 clock should thus come within a second a day, it would satisfy most 

 watch-makers ; and that as a matter of fact they ordinarily do change 

 their " regulators " several times a year — we have little difficulty in 

 accounting for the wide-spread ignorance of theory among them. To 

 this may be added the consideration that there is no money in know- 

 ing about these things, and that to know about them takes time that 

 might become money. 



Again, we shall find our jeweler almost equally ignorant of the 

 principles of compensation in the balances of watches. There are but 

 few of them, indeed, who can not tell the genuine balance from the 

 spurious, but there are hundreds of them who could not state, if life 

 depended upon it, why the brass must needs be on the outside and the 

 steel inside in such a balance, or why the converse arrangement would 

 not be equally good, or whether the screws in the rim have anything 

 to do with the compensation. 



If, then, those who might be expected to know know so little, 

 where shall we look for information ? In view of the general igno- 

 rance of this matter and interest in it, a plain and untechnical account 

 of the difficulties in the way of measuring time accurately with clocks 

 or watches, and the progress that has been made in obviating them, 

 may be profitable. 



The whole matter of the accurate measurement of time turns, of 

 necessity, on the manner of controlling the rate of escape of the 

 mechanism which indicates the time. Thus far there are only two 



