NOTES ON THE REFRACTIVITIES OF THE INACTIVE GASES 



WILLIAM RAMSAY, F. R. S. 



lu the course of a research ou the properties of argou^ Lord Ray- 

 LEiGH, (Proceediugs of the Royal Society, volume 59, p. 203), devised 

 a simple apparatus by meaus of whicli it is ])ossible to couipare the 

 refractivity of argou witli that of air. Siuce that time I hâve beeu fre- 

 qiieutly eugaged iu deteruiiuiug the dilfereut refractivities of the iuactive 

 constituents of the atmosphère; aud l hâve pleasure iu giviug a short 

 accouut of thèse experimeuts iu order to preseut a tribute to my frieud 

 Professor Lorentz, which rnay be of iuterest to hiui, aud to those who 

 hâve foUowed his liues of research. 



It will be seeu ou cousultiug Lord RAYLEiGirs paper, that the refrac- 

 tivity is uieasured iu the followiug uiauuer : Light from a paraflfiu lamp 

 passes through a fine slit, eut with a razor iu tiu-foil pasted ou glass. 

 The beaui is made parallel by passage through au achrouiatic plauo- 

 couvex leus of about 1 foot focal leugth. Tt theu di vides; the up])er 

 portiou passes through air, aiid, after extraueous light is eut otl* by 

 passage through two wide slits, it is brought to a focus by a leus similar 

 to the hrst, and the bands produced are viewed by a cyiiudrical leus of 

 very short focus. The lower portiou of the boam traverses two tubes o2 

 cms. long aud 2 mms. iu diameter, placed close together aud closed at 

 each end with plates of o])tically worked glass. Each of thèse tubes 

 contains oue of the gases to be examiued aud each is couuected with a 



