Masterpieces of Science 



relate to it. The last few years have brought 

 sure knowledge of a minute periodical shift of 

 her axis and a corresponding displacement of 

 the poles upon the surface of the globe. So far 

 as the accuracy of our present observations can 

 decide, this shift appears to be nearly regular; 

 and yet theory would rather indicate that for 

 various reasons it must be more or less irregular, 

 and accompanied by corresponding changes in 

 the rate of rotation or length of the day. It is 

 to be hoped that before very long we may become 

 able to detect the presence and amount of such 

 irregularities if they really exist, and it is not 

 to be disguised that some anxiety is felt lest 

 it should be found that we are already near the 

 limit of accuracy in astronomical prediction 

 actually approaching a boundary which cannot 

 possibly be overpassed. For if the earth, our 

 standard measurer of time, "goes wild" to some 

 appreciable amount, it is clearly impossible to 

 predict astronomical events within time-limits 

 closer than the extent of her vagaries unless, 

 indeed, some other time-measurer can be found, 

 steadier and more to be trusted, to take her place. 

 Doubtless, also, the years to come will correct 

 our knowledge of the dimensions of our globe 

 and of its mass and density. At present our 

 estimate of the distance between any two "well- 

 determined points" on opposite hemispheres 

 say, for instance, between the centres of the domes 

 of the observatories at Washington and the Cape 

 of Good Hope is uncertain by at least a thou- 

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