DEGLI SPETTROSCOPISTI ITALIANI 



133 



On a new class of absorption phenomena 



by J. Norman Lockyer, F.B.S. 



1. In the experiments on the absorptioa-spectnim of Na and K vapour heated iu 

 a red-hot tube, to which farther reference is made in separate notes, I bave obser- 

 ved phenomena quite new to me, some rough drawings of which I lay herewith be- 

 fore the Royal Society. As the phenomena are ouly momentary, I cannot answer for 

 the final accnracy of the drawings, nor bave I been able to represent the softness 

 of the gradations of shade. 



2. Iu the drawings, the red end of the spectrnm is to the left; the D line com- 

 mon to them ali is the iniage of a slit abont half aii iuch long, on which slit the 

 light falls from an electric lamp, through the tube and chamber in which the va- 

 pours are prodnced. The lower part of the drawings would generally represent, the- 

 refore, the spectrum of the less dense vapours were the vaponrs at rest. 



3. One of the phenomena referred to consists of what may be described as a uni- 

 lateral widening of the line D: the side absorption, however, is much less dense 

 that of the line; it is bounded by D on one side and by a curved line on the other. 

 In the Table XLVIII, Figs. 1, 2, and 3 will give an idea of this appearance in three 

 stages as it is frequently actnally seen, i, e, as the absorption travels up or down 

 the line it widens as shown. 



4. Figs. 4 and 5 give two variations sometimes observed — fig. 4 showing the 

 darkening in the absorption and an increased steepness in the curve; fig. 5 the si. 

 multaneous existence of apparently different ahsorptions, ali bounded by D on one 

 side, but by different cnrves on the other, and being of different intensities. 



5. Although, in the preceding drawings, I bave represented this nnilateral wide- 

 ning cxclnsively on the more refrangible side of D, I bave observed it on the other 

 thongh scarcely so frequently. 



6. Accompanyng these appearances, but generally best visible when the absorption 

 with cnrved boundary is visible on both sides of D, is a brilliant boundary repla- 

 cing the mere change of shade. 



7. At times the brilliant boundary is continuous across D, as shown in fig. 6; but 

 I append figs. 7 and 8 to show that the phenomena on either side of D are inde- 

 pendent of each other. 



8. At times, D puts on the appearance of the limiting line of a channelled-space 



Giornale di Scienze Kat. ed Econ., Voi. X. — 1874. 19 



