CHRISTIAN HUYGENS 71 



oscillation, since the force controlling it only comes from 

 the train, and is subject to variation in friction, whereas the 

 pendulum possesses its own controlling force in its invari- 

 able weight, and hence a fixed period of oscillation, which 

 is uninfluenced by the power of the train; the latter being 

 needed only to overcome the air friction of the pendulum, 

 which is less, the heavier the pendulum is made. A new 

 idea was brought into the old clock, which apart from the 

 hanging pendulum was not greatly changed in form, but the 

 effect was something entirely new: trustworthy measure- 

 ment of time. Huygens says himself, in his Horologium 

 Oscillatorium: 'Even if there is in the works themselves some 

 defect or other, even if the bearings turn less easily as a result 

 of change of temperature, as long as the movement of the 

 clock does not cease entirely, no irregularity or retardation 

 in motion is to be feared: the clock will either always measure 

 the time correctly, or not measure it at all.' It is not sur- 

 prising that, since the change in construction was so small, 

 existing clocks immediately received pendulums fitted to 

 them in place of the oscillating body. Since the year en- 

 graved on the dial, and giving the original date of construc- 

 tion, usually remained unaltered, the opinion later arose, 

 that these clocks had been made as pendulum clocks before 

 Huygens' time, but this opinion can be proved by the 

 literature of the period to be wrong.^ 



For navigation, good clocks were and are of the greatest 

 importance for the trustworthy determination of geographical 

 distances, and the correct measurement of position at sea. 

 But in this case the usual pendulum, dependent upon 

 gravity, was not satisfactory in spite of Huygens' special 

 efforts, on account of the oscillation of the ship. He there- 

 fore proceeded to use elastically controlled pendulums for 



1 See Horology, by J. E. Haswell (1928), p. 25. In England a model in 

 the S. Kensington museum of a 'pin-wheel' escapement is usually re- 

 ferred to as being prior to Huygens. [Trans.] 



