WEIGHING THE EARTH. 

 By a. E. Blackman. 

 (Read October loth, 1910.) 



ABSTRACT. 



Of the many methods adopted up to tlie present for 

 accornpHshing this, none appear to me to be" as free as 

 they might be from many sources of error. 



As in all other scientific systems of taking measure- 

 ments, especially those in which the object of measurement 

 is not directly comparable with our established units, 

 special instruments have to be constructed by which 

 certain measurements are taken, these serving us by the 

 aid of the known laws involved with sufficient data to 

 make calculations from which we derive the answer 

 sought. 



This necessitates the selecting of a method out of the 

 possible many at our disposal, which, with the same 

 degree of care taken ^ in those measurements, will lead, 

 all things considered, to the most reliable result. 



The less the number of such measurements, and the 

 larger the parts measured (the size of a part here refers 

 to it as a multiple of the smallest portions of it capable 

 of measurement), as a rule, the more dependable ^must 

 be the result. 



From the aljove considerations I conmiend the 

 following method : — 



Newton's discovery that all particles of matter attract 

 all others by forces varying inversely as the square of 

 their distances leads to the following principles upon 

 which depend the reasons for the special arrangements 

 and calculations necessary to our purpose. 



All material bodies attract one another directly and 

 jointly as their masses, and inversely as the squares of 

 their distances. 



