TO SPECTROSCOPIC MEASUREMENTS. 



19 



In order to show conclusively that the effect of density may be neglected 

 in the foregoing observations, as well as to ascertain the law governing the 

 broadening of spectral lines, by pressure or density, a series of observations 

 was made on the red hydi'ogen line at varying pressutes, with the results 

 shown in Fig. 19a, Plate Y.* 



From these curves the following table was calculated : 



* The numbers against the curves denote pressure in millimeters. 



