46 



SCIENCE 



[N. S. Vol. LI. No. 1306 



Of course if the train runs eastward, the 

 required supporting force will be less than if 

 the train were at rest. In particular, if the 

 eastward train-speed is about 16 V, S will be 

 zero. 



There are thus two speeds, one westward of 

 about 18,700 miles per hour, and one eastward 

 of about 16,700 miles i)er hour, at which the 

 " weight " of the body as measured by an ob- 

 server on the train (that is, the tension in 

 the supporting string S) would be zero. 



Edwaed V. Huntington 

 Haevard Unxversity, 

 November 22, 191& 



AN ODD PROBLEM IN MECHANICS 



To THE Editor of Science : In a recent dis- 

 cussion the writer offered the following prob- 

 lem which seems to be new and of interest, 

 judging from the answers and lack of answers. 



Assuming the earth to be a perfect sphere, 

 the net weight of a body on this earth is Gr — 0, 

 in which G is the force due to gravity and C 

 the centrifugal force due to the rotation of 

 the earth. Hence the net weight of a body at 

 the equator when moving east at a velocity 

 (relatively to the earth) equal to that of the 

 surface of the earth, about 1,000 miles per 

 hour would be G — 40, that is, less than when 

 at rest, while when moving west at the same 

 velocity it would be G, that is, greater than 

 when at rest. 



If therefore a flywheel were revolved at the 

 equator with that circumferential speed and 

 in a horizontal plane, the northern part 

 moving east, it would seem to follow that it 

 will tilt to the south, as the southern half 

 should be heavier than the northern half. 

 Due to a time lag the tilting might be to the 

 southwest. It is here assumed that its gyro- 

 scopic tendency to get into a vertical plane 

 has been duly counteracted and may be 

 neglected. 



Or stated in a different form, suppose a 

 light disc be revolved at this speed in a 

 vertical plane at the equator, and to have two 

 equal symmetrically placed, heavy masses on 

 its rim. When the plane of rotation is north 



and south it woidd be dynamically balanced, 

 but when that plane is east and west it would 

 seem to follow that the masses at the moment 

 they are at the bottom would be heavier than 

 when at the top and if so the disk would be 

 unbalanced dynamically, vibrating with a 

 period double that of the period of revolution. 

 Its center of gravity would oscillate below its 

 center of rotation. 



It is acknowledged to be possible, theoret- 

 ically at least, to move a mass so rapidly over 

 the earth that G = hence the net weight 

 then is zero ; it would then go on encircling the 

 earth, if the air friction were eliminated; the 

 moon is an illustration. At lower speeds 

 therefore there should be a part of this loss 

 in effective weight. 



The two cases cited, if the results are as 

 described, would afford a basis, theoretically 

 at least, for a mechanical compass, like the 

 gyroscope compass. 



Oael Heeing 



Philadelphia, 

 October 27, 1919 



QUOTATIONS 



SCIENCE AND THE NEW ERA PRINTING 

 COMPANY 



Old wood to burn, 

 Old books to read. 

 Old wine to drink. 

 Old friends to cling to. 



It takes a near-millionaire to burn "old 

 wood" on his hearth these days; "old books" 

 are the delight of the bibliophile, but are poor 

 stuff in producing the wherewithal of a print- 

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 only a hollow mockery — 



But " old friends to cling to ! " Ah ! there is 

 the kernel, the gem that glitters from the quad- 

 ruplet ! 



All of which is jusit by way of introduction 

 to an acknowledgment of one of the most 

 gracious compliments ever paid to The New 

 Era Printing Company. 



As the year fast nears its close, it marks the 

 twenty-fifth anniversary of The New Era 

 Printing Company's production of Science, a 

 magazine whose contributors enibrace the 



