May 20, 1910] 



SCIENCE 



161 



per cent, of those children who have de- 

 fective hearing have often been found to 

 be dullards. Also those suffering from 

 adenoid growths are likely to be found in 

 the class of dull children. And while 

 myopic children are often found among 

 those more precocious and studious in 

 school work, this due, perhaps, to their 

 lack of normal interest in things out of 

 doors and muscular activities, those with 

 eye defects often seem hopelessly dull. 



It is evident that we are dealing with a 

 problem fundamental in pedagogy and 

 school hygiene. Every parent knows the 

 leaden stupidity that at times comes over 

 children, and every teacher has doubtless 

 had experiences with at least a few eases 

 of it in chronic form. This is the one de- 

 fect which to many teachers seems hopeless. 

 The only redeeming thing about stupidity 

 seems to have been discovered by a Ger- 

 man, who with rather a labored attempt at 

 wit has said that the stupid children will 

 make invincible soldiers, because the gods 

 themselves fight in vain against stupidity; 

 but what is impossible to the gods of peda- 

 gogy is sometimes possible to Hygeia. 

 When stupidity is due to a defect of the 

 sense organs, the difficulty can sometimes 

 be removed by the simple device of seat- 

 ing the pupil in a favorable position; a 

 surgical operation for an adenoid growth 

 has removed the cause of stupidity in the 

 case of many children; and frequently 

 what the stupid child specially needs is 

 enough to eat, or sufficient sleep, or rest 

 from work imposed out of school hours, or 

 perhaps the mere stimulus of social suc- 

 cess. In any case the cause should be 

 sought. 



Thus the simple problem with which we 

 started leads out into the wider problems 

 of social hygiene and social pedagogy ; and 

 here I must leave it with the hope that it 



will be considered by teachers and studied 

 further by investigators. 



Wm. H. Burnham 

 Claek Univeesity 



THE PRINCIPLE OF RELATIVITY 



At the recent Boston meeting of the 

 American Physical Society there was so 

 much general interest in the principle of 

 relativity and so many questions were 

 asked me personally by those who had 

 given the subject very little attention, that 

 it seems timely to give a brief introduction 

 to the subject on a somewhat simpler basis 

 than I think has yet been attempted. The 

 method employs several of the "non-math- 

 ematical" conceptions first introduced by 

 Lewis and Tolman, but I think the demon- 

 strations will be found even simpler than 

 theirs. 



The principle of relativity is one at- 

 tempt, and by far the most successful at- 

 tempt as yet, to explain the failure of all 

 experiments designed to detect the earth's 

 motion through space, by its effect on ter- 

 restrial phenomena. It generalizes this 

 universal negative result into its first pos- 

 tulate, which is, ihe uniform translatory 

 motion of any system, ccm not he detected 

 iy an observer traveling with the system 

 and making observations on it alone. 



The second postulate is that the velocity 

 of light is independent of the relative veloc- 

 ity of the source of light and observer. 



At the very outset, it is important to 

 realize that we have no long-standing ex- 

 perience with systems moving with veloci- 

 ties comparable with that of light, and 

 therefore that primitive intuition may not 

 be the very best guide in first introducing 

 us to them. "We might easily imagine a 

 peasant scorning the suggestion that the 

 dimensions of a rigid body changed with 

 the temperature, and declaring, on being 



