723 



the tube takes place in a soinewliat mis} mmetriccil way. For this 

 reason, and at the same time on account of the huge differences of 

 temperature which must necessarily exist in the Wood tube, at 

 which there can be no question of saturate vapour, I did not under- 

 take quantitative measurements. 



Finally in order to be able to carry out njcasurements whicli 

 should be liable to interpretation, I have generated the sodium vapour 

 in a vertical glass tid)e, which was first provided with some pieces 

 of sodium, then evacuated down to about 0.001 ni.m. of mcicuiy, 

 and sealed to. This tube was uuiforndy heated all over its length 

 by an electrical way, so that the temperature may lie assumed to 

 be the same at all places, and accordingly the sodium vapour to be 

 saturate. In the enclosure there were made two apertures, through 

 which the light fell in horizontal direction. As the glass gradually 

 clouded somewhat at these places, I later on applied side tubes which 

 were also electrically heated, while a wider glass tube was also 

 used. The bore of the tube, with which 1 carried out ray final 

 measurements, amounted to 28 mm. For a reason to be stated later, 

 this tube was placed between object glass and eyeglass of the reading 

 glass. Of course the image suffered by this, but nevertheless it was 

 possible to measure the distances of the components. 



The phenomena which I observed in this way were qualitatively 

 in perfect harmony with what I had seen bj' means of Wood's tube, 

 and during the blowing in of the soda mist into the arc. On rise of 

 temperature the distance of the components increases, while |hey 

 become less sharp at the same time. Up to almost 300° the distance 

 can be very well measured, the results of these measurements have 

 been represented in the curves B, and />,,. At higher temperature 

 the width is too large to be investigated by means of the échelon 

 spectroscope, the phenomenon becoming veiy vague then, so that 

 the absorption maxima are clearly perceptible on slight magnitication 

 only, the light intensity is only little greater then between the absorption 

 maxima than in the maxinui themselves. The greatest width measu- 



o 



red amounts to about 0,21 A.Ü.. as is visible from the figure. 

 The resolution is always greater for D^ than for D^ ; the curves 

 indicating the course in the two cases run perfectly parallel. On 

 the whole the components of YJ, are somewhat sharper than those 

 of A ; ^^ J^i the component lying to the side of the red is the 

 stronger and sharper, of D,, that which lies to the side of the violet. 

 I think I have been able to obserx e with pretty great certainty that 

 the two components of /J, are each double, so that the absorption 

 region would be bounded here by two absorption maxima on either 



