On the Measurement of Time. 367 



for this purpose : later on, up to our days, sun-dials were 

 constructed, and improved with the aid of* Euclidean geo- 

 metry. And the first step (not the last, as Dr. Campbell 

 thinks) was here emphatically the picking out of some 

 grandiose phenomenon and declaring it to go on or to evolve 

 " uniformly," " equably.''' Nor did these principles of chrono- 

 metry suffer any serious shock from the great Copernican 

 reform. Somehow our forefathers chose to declare the 

 Earth's revolution round the Sun and its spinning motion 

 about itsown axis as "uniform," and continued to subdivide 

 the associated angles. Manifestly the sun-dials, or their 

 prototypes, continued to show the hours in spite of the 

 modified standpoint. Yet these natural solar clocks had 

 their bad side, which perhaps is best expressed by the old 

 and beautiful words to be still read on some sun-dials in 

 Italy : 



Horas non numero nisi serenas. 



Other time-keepers were, therefore, invented and con- 

 structed in very early times, that is to say, even much before 

 Copernicus, whom we mentioned only incidentally — and in 

 all of them the said two features played a dominant role. 

 I do not propose to enumerate here all such old chrono- 

 metrical devices ; nor have I the required historical erudition. 

 But one such device attributed to Alfred the Great, who 

 ruled over the West Saxons (871-901), I cannot pass here 

 in silence, since it seems particularly characteristic in 

 relation to our subject. According to what my little boy 

 heard in his school *, Alfred the Great had good tall candles 

 (of what stuff I know not) made for him, and, confiding 

 no doubt in the uniformity of their burning down, divided 

 them into equal segments, and thus knew the time in day or 

 night. But apart from the "nisi serenas" condition, the 

 solar clocks had the defect of not being applicable to short 

 time spans (certainly not to our " seconds,"* and not even 

 to our "minutes"), and the other famous kind of natural 

 time-keepers, the human heart or "pulse/" was too often 

 affected by passion or disease to retain permanently the title 

 of uniform (here uniform succession of discrete pulse-beats). 

 Thus the mediaeval physicist and astronomer had recourse to 

 a variety of artificial chronometric devices. Even a long 

 time before the Renaissance complicated wheel machines 

 were constructed as clocks, but none of them was "well 

 regulated " until the times of Galileo and, more especially, 



* I have no other means at the moment to verify the historical truth 

 of this report. 



