218 THE RANGE OF NATURE'S OPERATIONS. 



OF THE RELATION BETWEEN LIGHT AND OUR SCALE. 



This leads us to consider the relation in which light stands to our 

 survey. It is useful to do so, since it gives unity to our survey to c-on- 



FiG. 6. 

 Stellae Distances. Planetary. 



000 000 00 00 00 



9 467 94 6 7 



^is the distance ^is the distance whicli 



which light will travel in light will travel in one year, 

 one hundred millions of 

 years. 



sider how our table is related to light, which in one direction reaches, 

 by the minuteness of its waves, the border land of molecular magni- 

 tudes and in the other direction, by reason of its great speed, can trav-, 

 erse innuense distances in periods of time which we can grasp. The 

 relationship is exhibited in the lower section of fig. 1, which gives the 

 times which light must have to enalile it to reach us from the distances 

 represented by a unit in each of the indicated parts of the table. The 

 information there recorded may be supplemented by that added in fig. 6. 



ON THE MEASUREMENT OF TIME. 



The same table may be employed for measuring time. Intervals of 

 time for the purposes of physical inquiry are best measured by the 

 distances over which light in the open ether would travel in those 

 periods. In this way measures of distance become measures of dura- 

 tion upon that scale upon which a metro-eight (which is the same as 

 the centimo-ten) represents one-third of a second — a scale which in 

 practice is found to be very convenient, especially for the study of 

 molecular physics. To represent a second of time on the diagram, 

 insert the digit 3 instead of the cipher which occupies the middle place 

 in the planetarj- group of positions. In this way of measuring time 

 300 meters of time (1,000 feet^) is the same as the millionth of one 

 second. 



OF MOLECULAR EVENTS. 



In molecular physics the periods of time which have to be dealt with 

 are almost inconceivably shorter than any to which we are accustomed. 

 The unit of time which the present writer has found the most generally 

 convenient is the micron of time— the time which light takes to advance 



'That is, 1,000 metric feet. In science the yard of 9 decims, the foot of 3 decims, 

 and the inch of 25 milUuis should always be used instead of the so-called "imperial" 

 measures of the same names. Here the old or imperial measures are to the new or 

 metric measures in the ratio of 101.6 to 100, or in the ratio of 63 J to 62 J, or in the 

 ratio of 127 to 125. It may be useful to point out that lathes and dividing engines 

 provided with Whitworth screws the pitch of which is known in imperial inches may 

 be made to produce screws or graduate scales in the metric measures by simply intro- 

 ducmg two change-wheels, one with 127 and the other with 125 teeth. 



