REFRACTIVE INDICES OF TIIK ELEMENTS. 



problem will l>e solved till we are in possession of the iiuliceH of a large number of 

 simple compounds, determined in the gaseous state to a degree of accuracy higher 

 than that which can be claimed for the existing determinations. 



The list of the obligations which I desire to acknowledge is a long one. I have to 

 thank Professor TBOITTON for his kindneas in admitting me to the Physical Laboratory 

 of University College, I-iondon, and in placing at my disposal all the resources at his 

 command. To him, to Assistant Professor A. W. PORTKR, to Sir WH.LIAM RAMSAY, 

 and to every Member of the Chemical and Physical Staff of University College, I 

 owe a debt of thanks for their unwearying kindness and invaluable help. I have 

 already expressed my obligation* to M. HKNIU MOIFWAN and his staff, for their 

 assistance in the work on fluorine. To Mr. lln.<.i:it. and after his death, to 

 Mr. TWYMAN, I am deeply indebted for the interest they have shown in the 

 preparation ot the refractometer tubes, and for the skill and accuracy of their 

 workmanship. Finally, I have great pleasure in again expressing my cordial thanks 

 to the Government Grant Committee of the Royal Society for the contribution they 

 have made towards the expenses involved in the work. 



