-]€> THE POPULAR SCIENCE MONTHLY, 



The student will soon find that different persons, in singing the 

 same note, as nearly alike as they can, will produce flames of very dif- 

 ferent forms. This is because the voices dift'er in the number and rela- 

 tive intensities of the simple sounds which form them. 



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THE EADIOMETER. 



By J. W. PHELPS. 



OOME twenty-five years ago, when Foucault's ingenious experiment 

 KJ for proving the earth's motion on its axis was in vogue, the idea 

 occurred to us that that fact might be proved in another way. Fou- 

 cault's method, it will be remembered, consisted in the vibration of the 

 pendulum in a fixed direction, the earth's motion being disclosed by the 

 angular deviation of a given chalked line from that direction. In the 

 pursuit of our own method we conceived the idea — which, though a very 

 simple one, was not more simple than some others have been of experi- 

 mentalists, both before and after the fact — that, if a small needle, say of 

 dry wood, could be suspended from its middle by a torsionless thread, 

 and be excluded from the air, it would retain any fixed direction, while 

 a parallel line under it would change from that direction in proportion 

 as the horizon turned from west to east. In order to carry out this 

 idea we suspended a wooden needle by a thread of spider's web from 

 the underside of the cork stopper of a large glass jar, and for addi- 

 tional security against possible currents of air placed the whole inside 

 of a large chest. 



On going to this chest to ascertain the result of our experiment, 

 which we happened to do by night, and had to take a light with us, we 

 were surprised to see, the moment we raised the lid, the needle begin 

 to move ! Our first thought was that we had made a great discovery . 

 that light was a material substance, and that enough of that substance 

 could emanate from one small candle to move a needle when freely sus- 

 pended, in an horizontal position ! The weight of light, of course, we 

 knew must be infinitely small, if it had any weight at all ; but then, by 

 multiplying what little weight it might have by its known amazing 

 great velocity, we did not know but that the motion which we wit- 

 nessed might be produced in the way supposed. A little examination, 

 however, into the matter, soon convinced us that our first impressions 

 were erroneous. 



We preserved the glass jar with the needle suspended in it for 

 many months ; and the most astonishing thing about it to us was that, 

 however much the needle turned, though at times it would spin round 

 with great and long-continued velocity, the thread of spider's web never 



