468 



SCIENCE 



[N. S. Vol. XXXVIII. No. 979 



Similarly tiie moving system may represent 

 an earth always in uniform translation with 

 respect to the sun. At two stations upon the 

 earth sixty earth miles apart are fixed a clock 

 and an observer. A sun-man can see only 

 one earth clock and earth-man at one time, 



light particle in the ratio of two to three. We 

 must, therefore, interpret our model as a mag- 

 nifier of nature's facts with respect to space 

 and time. 



Suppose A and B upon the sun wish to syn- 

 chronize their two clocks which are exactly 



r 



namely, at the instant earth-man passes sun- 

 man, and vice versa. Also, only at the in- 

 stant an earth-man passes a sun-man can 



Fig. 3 



either make an observation and a comparison 

 of the length and time standards used upon 

 sun and earth. 



alike in every respect and perfect mechanisms. 

 When A's clock reads 12 (Fig. 2), he sends 

 out the light signal which, reflected by the 

 mirror at the 60-mile station, returns after 

 the hand of A's clock has moved through 

 12 -f- 4, or 16 hours. Assuming that it took 

 the light sig-nal eight hours to go one way, A 

 writes B to be on the lookout; the light signal 

 will again leave at 12 and should reach B at 

 8 (Fig. 3). When the signal arrives, B sets 

 the hand of his clock at 8, and the two clocks 

 are now in synchronism, and may be used by 

 both observers to establish simultaneous mo- 

 ments of time. 



The course pursued by A and B upon the 

 sun at rest is followed by A^ and B' upon the 





r 



Fig. 4 



As the naturalist's picture of a microorgan- 

 ism misrepresents nature as to size, so our 

 model is, in this respect, also a " nature-faker." 

 The orbital velocity of our earth is to the 

 speed of light in interstellar space as one is to 

 ten thousand ; but the model arbitrarily repre- 

 sents the earth's velocity to the velocity of the 



earth in motion. With their own foot rule 

 A' and B' have placed their two clocks sLxty 

 miles apart, and they too (Fig. 4) find that six- 

 teen hours is required for the passage of the 

 light signal from A' to B' and return, and that 

 B' must set the hand of his clock at 8 (Fig. 5) 

 when the light signal sent by i.' at 12 reaches 



