368 Dr. L, Silberstein on the 



Huyghens. Properly speaking, these " chefs- d'oeuvre 

 d'agencement cinematique de mouvements, 5 ' as Jules Andrade 

 calls them, were not ' ; regulated " at all ? i. e. were felt not to 

 be worth the name of " uniformly going/' not keeping pace 

 with the heavenly clock. The now undisputed merit of con- 

 structing the first clock in the modern sense of the word is 

 (due to Huyghens, although it was Galileo's discovery of the 

 r isochronism " of small pendulum oscillations which he 

 utilised in such an ingenious way. Yet, before Huyghens's 

 invention, Galileo, who was the first to measure compara- 

 tively short time-intervals, constructed his own clock for the 

 sake of his famous investigations on falling bodies, a water- 

 clock that is, but more precise than the water- or sand-clocks 

 and the " mechanical " clocks which he inherited from his 

 predecessors. Galileo's own clock is, in the present con- 

 nexion, as instructive as the burning candle- of Alfred the 

 Great. It consisted of a vessel or water-basin of large 

 section having a very small hole in its bottom, to ensure, no 

 doubt, the u uniformity " of the outflow of that liquid. This 

 was his first care. The remainder of the procedure was 

 again in full harmony with our statement ; Galileo measured 

 the volume of the water (by weighing it, that is, but this only 

 to make the volume measurements more precise), and he 

 spoke of £-=1, 2, 3, etc., as proportional to the number of 

 equal volumes of water; this is equivalent to measuring lengths 

 along the axis of a well-calibrated and narrow cylindrical 

 vessel, if he had one. Galileo's times (the t in his great 

 law s-^-t 2 ) were proportional to these volumes or ultimately 

 lengths, read on a metrical scale. That the same principles 

 can be instantly traced in all our modern clocks, watches, 

 and chronometers, needs scarcely to be insisted upon. 



But they occur perhaps in their purest form in those 

 modern instruments which serve to measure very short 

 times, even down to one-millionth of a second, and perhaps 

 a little less. I have in mind Siemens's high-speed spark 

 chronograph. It consists, in essence, of a little revolving 

 drum of good steel driven by a carefully finished clock-work. 

 Against this drum, which we used (1897) to cover tightly 

 with a strip of paper blackened with a turpentine lamp soot, 

 is mounted an isolated platinum electrode. Sparks correlated 

 with the events in question pass between the platinum point 

 and the spinning drum and leave marks (little craters) on its 

 blackened surface. The clockwork is then stopped and the 

 drum turned round slowly by a niierometric screw, while 

 the marks are viewed through an appropriately placed 

 microscope. Their angular distance, as read on a subdivided 



