Chemical and Physical Notes 1 1 3 



Supposing that we take the hypsometer to these latitudes, 

 and that we determine the boiling-point of water with every 

 care at each latitude at the sea-level when the standard baro- 

 meter at o C. stands at 735'5 mm., and we find that the 

 boiling-point is the same, namely 99X)87 C. at all these 

 latitudes, then we conclude that the true pressure of the 

 atmosphere at each of the localities is 1000 grms. per square 

 centimetre. But we know from the geodetic determination 

 of the figure of the earth that the sea-level is nearer the 

 centre in lat. 70 than it is in lat. 45, and nearer in lat. 45 

 than in lat. 10. If the earth is homogeneous the force of 

 gravity must be greater at lat. 70 than at lat. 45, and at 

 lat. 45 than at lat. 10. But from the identity of the height 

 of the barometer at the three localities we know that the mass 

 of the atmospheric column is the same at the three places, and 

 from the identity of the boiling-point of water we know that 

 the weight of the three columns or the atmospheric pressure is 

 the same in the three places. As the force of gravity depends 

 only on the mass of the attracting body and on the distance 

 of its centre from the attracted body, and we find that when 

 this distance is varied in a certain measure no alteration is 

 produced in the effective force of gravity, the conclusion is 

 necessary, that the effect of variation of distance has been 

 exactly compensated by variation of the effective attracting 

 mass. In the example taken we find the force of gravity in 

 lat. 10 greater than it should be, and in lat. 70 less than it 

 should be. 



As the attraction of the whole earth on a particle at its 

 surface is the sum of the attractions of all the particles that 

 make up its mass ; and as the attractive force of each particle 

 of the earth's mass on the particle at its surface is inversely 

 proportional to the square of its distance from that particle, 

 it is evident that the particles in the vicinity of the attracted 

 body will exercise, mass for mass, a much greater attraction 

 on the body than the particles that are more remote, for 

 instance, at the opposite end of the diameter of the sphere. 

 Therefore, the occurrence of rocks of relatively high density 

 near the surface in a locality may easily cause an exaggerated 



