PHYSICS. 



By GEORGE F. BARKER, 



Professor of Physios in the University of Pennsylvania, Philadelphia. 



GENERAL. 



The activity in Physical Science during 1877 has been 

 fully equal to that of any former year. The distinguished 

 physicist, Professor Sir William Thomson, in his address as 

 president of the Mathematical and Physical Section of the 

 British Association at the meeting at Glasgow, September, 

 1876, after speaking in laudatory terms of Americans, Amer- 

 ican science, and the Centennial, discusses anew the question 

 of the solidity of the earth, and gives the results of new cal- 

 culations from precession and nutation to prove it, under- 

 taken in consequence of suggestions made to him by Pro- 

 fessor Newcomb, of Washington. 



Main has claimed and with justice too, apparently with 

 reference to the discussion in England concerning the mean- 

 ing of the word "force," that it was used by Newton as the 

 English equivalent of the Latin word vis, and not alone of 

 vis impressa, as is maintained by Tait. When Newton 

 wrote vis insita, vis motrix, vis gravitatis, vis centrifuga, 

 he must have had in mind for each of these their ordi- 

 nary English equivalents, in which vis always means force. 

 This use of the word is by no means loose and inaccurate ; 

 it is rather general and comprehensive. Main closes by 

 saying: "Some English mathematicians wish to have this 

 valuable word all to themselves for a special technical 

 sense; Newton claims no such monopoly, nor is it claimed 

 at all by foreign mathematicians, nor conceded by meta- 

 physicians ; nor is the claim to this monopoly likely to be 

 conceded until a better title to it has been shown." 



Matthey has presented to the French Academy the bar 

 of platinum -iridium made for the four- meter standard, to 

 the order of the International Geodetic Association. To 

 make it, 450 ounces of platinum and 55 of iridium were 



