WEIGHING THE WORLDS 



detected, and the slightest tremor, as from some one 

 walking in the house, put the apparatus quite out of 

 commission. 



The final result of Professor Boys' test was to 

 give the figures 5.527 as the average density of the 

 earth in the comparison with water. Still more re- 

 cently Mariaschein of Bohemia has repeated Profes- 

 sor B'oys' experiments and fully confirmed his results, 

 so it seems fairly established that the density of the 

 earth does not differ greatly from the figure given. 

 The weight of our globe, then, is a trifle more than 

 five and one-half times what it would be if it were 

 composed entirely of water. Stated in tons, the 

 weight runs into unmeaning figures; but the aggre- 

 gate furnishes a useful unit in computing the bulk of 

 the other planetary bodies. When stars are in ques- 

 tion, the bulk of the sun furnishes a more convenient 

 unit as we shall see. To estimate the bulk of a star 

 in terms of the earth's mass would be like measuring 

 the weight of an elephant in grams, or computing 

 the life-time of a man in hours. 



Reference should be made to earth-weighing tests 

 of another kind made by Airy and others by compar- 

 ing the pendulum swing at the earth's surface and in 

 the depths of mines; and to Professor Poynting's 

 wonderfully delicate tests with the balance, in which 

 a fifty-pound weight was seemingly given increased 

 weight by bringing a 350-pound mass directly be- 

 neath the scale. Professor Poynting's experiments 

 were of such delicacy as to be equivalent, he tells us, 

 to balancing the entire British population of 40,000,- 

 000 individuals against an equivalent weight, and 



