466 



SCIENCE 



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



tarsus with those above and below, so that 

 the tarsals act like epiphysial pads. Only 

 in mammals epiphyses are universal. Tibia 

 and fibula having their own, the pro- 

 nounced joint is cruro-tarsal and all the 

 tarsals could be used for a very compact, 

 yet non-rigid arrangement. The advan- 

 tage of a cap, not merely the introduction 

 of a separate pad, is well recognized in 

 engineering. 



Why is it that mamLmalian material can 

 produce what is denied to the lower classes ? 

 In other words, why are there still lower 

 and middle classes 1 Why have they not all 

 by this time reached the same grade of per- 

 fection? Why not indeed, unless because 

 every new group is less hampered by tradi- 

 tion, much of which must be discarded with 

 the new departure; and some of its energy 

 is set free to follow up this new course, 

 straight, with ever-growing results, until in 

 its turn this becomes an old rut out of 

 which a new jolt leads once more into fresh 

 fields. H. P. GiiDow 



TEE NEW BELATIVIT¥ IN PE¥SICS 



Ever since Newton's corpuscular theory of 

 light was supplanted, early in the nineteenth 

 century, by the theory that light travels in 

 waves through ether as sound through air, 

 physicists have been endeavoring to obtain 

 direct experimental evidence about this in- 

 visible, imponderable ether. 



The earth sweeps through space with a 

 velocity of about 2,000 miles a minute; if 

 ether fills all space, it should be possible with 

 the delicate instruments now in our posses- 

 sion to detect an ether drift, an optical effect 

 caused by the motion of the earth through the 

 ether. 



Among others. Professors Michelson and 

 Morley' tried to detect this ether drift experi- 

 mentally, but obtained purely negative results. 

 Although they failed to get evidence of an 

 ether, they did obtain new physical facts of 



^ Silliman's Journal, 34: 337, 1887. 



an even greater importance, which have caused 

 us to readjust our concepts of space and time. 



Let us assume that the sun and earth are 

 at rest in space; it then takes a beam of light 

 about eight minutes to travel through space 

 from the sun to the earth. 



If we assume that both sun and earth are 

 in uniform translation through space, that is, 

 that both are in motion along the same 

 straight line, we would expect, since the 

 velocity of light can not be increased or dim- 

 inished by motion of its source, that a light 

 beam would be longer on its way from sun to 

 earth when it travels in the direction of the 

 motion, and that the light beam would be a 

 shorter time on its way when it travels counter 

 to the motion; in traveling with the motion 

 the light beam would overtake the earth ; when 

 the direction of the motion is reversed, earth 

 and light flash would meet. 



These deductions, according to the principle 

 of relativity, are not valid, for the facts pre- 

 sented by Michelson's experiments show us 

 that the number of seconds that a light flash 

 is on its way can neither be increased nor 

 diminished when the interstellar space through 

 which the light has to travel is arbitrarily in- 

 creased or diminished by giving source and 

 observer the same uniform translation. 



Newton based his mechanics upon absolute 

 space and time,' " not that which the vulgar 

 associate with sensible objects." Clerk Max- 

 wel? said: "All our knowledge, both of time 

 and place, is essentially relative." Yet he 

 could not free himself from the Nevptonian 

 mechanics, and it was not until 1905 that 

 Albert Einstein'' repudiated the word absolute, 

 and out of the " vulgar " ideas of space and 

 'time developed the modern theory of rela- 

 tivity. Einstein was then an employee in the 

 patent office at Bern, and it is but fitting that 

 in Switzerland, which has furnished the world 

 with so many timepieces, new thoughts with 



' Newton, ' ' Prinoipia, " 1 : 8, 1822. 



"Maxwell, "Matter and Motion," p. 30 (Van 

 Nostrand ed., 1892). 



* AnrMlen der Fhysih, 17: 905, 1905; Jahrbuch 

 der Badioalctivitaet und Electronih, 4: 411, 1907. 



