1 5tt Scien tific Intelligence. 



obtaining each sodium line with a prominently double aspect by 

 manipulating the flame, the magnet is excited, and the dark band 

 in the midst of each sodium line is then seen to widen out con- 

 siderably in the region of most intense magnetisation, while a 

 bright intrusion line makes its appearance. On closer examination 

 this new line is seen to be double, by reason of a dark division 

 down its middle; and I apprehend that with still more magnetic 

 power this dark band might itself open out into two ; but this 

 last phenomenon I have not yet observed. 



The whole sodium group is thus seen as if it were octuple. 

 The effect is not due to a mere mechanical disturbance or re- 

 arrangement of the gases .of the flame by the agency of magnet- 

 ism; because a nicol, placed in the rays emanating transversely 

 to the magnetic lines of force, cuts off. nearly all the visible mag- 

 netic effect when oriented so as to get rid of light whose plane of 

 polarisation contains the lines of force — that is, of oscillations or 

 revolutions whose electrical components are across or around the 

 magnetic lines. That it does not cut off every trace of the effect 

 appears to be due to the fact that the field of force is not strictly 

 uniform, and so its lines are not strictly parallel. 



The following is a summary of the different appearances that 

 may be seen according to the state of the flame and the strength 

 of the field : — 



At low temperature, and with the flame forward in the field, 

 when each sodium line is sharp and single, magnetism widens it, 

 and with a little more power doubles it, causing a distinct dark 

 line down its middle. The same effect occurs with lithium and 

 thallium lines. 



At higher temperature, and with the flame partially behind the 

 field, when each sodium line appears as a broad hazy-edged 

 double, magnetisation greatly widens the doubling, pushing 

 asunder the bright components very markedly : stronger magne- 

 tisation reverses the middle of the widened dark band, giving a 

 triple appearance ; stronger magnetisation still reverses the mid- 

 dle once more, giving a quadruple appearance to the line. In 

 every case a nicol, suitably placed, cuts off all the magnetic effect 

 and restores the original appearance of the line. 



A curious circumstance is that although both lines D x and D 

 show the same effect, D 2 , i. e., the less refrangible line, shows it 

 best and most sharply. I should describe the effect on D 2 as a 

 coarse widening ot considerable amount, but without very clear 

 definition ; whereas the widening of D x , though perhaps no greater 

 in amount, is decidedly better defined. There is no doubt but 

 that, with my grating, D^ is the line at which one finds oneself 

 usually looking in order to see the details of the change best ; 

 and I can hardly suppose this to be subjective to the grating. I 

 hope to show the effects at the soiree next Wednesday. 



[The same thing is seen when salts of lithium or of thallium 

 are introduced into the flame, and the components of the doubled 



