PHILOSOPHICAL SOCIETY OP WASHINGTON. 89 



49TH Meeting. May 24, 1873. 



The President in the Chair. 

 Lieut. C. E. Button read a memoir 



ON GEOLOGICAL TIME. 



.50TH Meeting. June 7, 1873. 



The President in the Chair. 

 Mr. S. Newcomb made a communication 



on the mechanical EEPRESENTATION op a problem IN LEAST 



SQUARES. 



( This paper is published in full in Monthly Notices of the Royal Astronomical 

 Society, November, 1873.) 



Mr. H. H. Bates read a paper 



ON THE motion OF A PARTICLE TOWARDS AN ATTRACTING CENTRE. 



Mr. R. Keith read a paper 



ON THE NATURE OP THE FORCE OF GRAVITATION. 



51sT Meeting. June 21, 1873. 



The President in the Chair. 

 Mr. J. E. HiLGARD made some remarks 



on the air thermometer of prof, jolly, 

 exhibiting also one of those instruments. The same gentleman 

 also made the second communication 



on the recent determination op the longitude between 

 paris and greenwich. 



Mr. J. J. Woodward then exhibited, with appropriate remarks, 

 the spectra of certain metals and gases. The apparatus used 

 was a four-prism spectroscope by Browning, with a six-inch in- 

 duction coil by Ritchie and a condenser by Ladd. He had also 

 upon the table several smaller spectroscopes, with which the spec- 

 tra of various chlorides were shown. 



