104 K. TAKIZAWA. 



it the groiij) A) into the centre of the lield by inereayino- the thickness 

 of the air lihn, so as to form a central dark spot, and examine the 

 spectrum of a small portion of it by a prisnn we ol)serve a series of 

 dark bands l)etween which there is a series of curved dark l)ands. 

 The straight bands are those formed by the mica iihn, and the curved 

 ones are those formed by the Xewton's ring air film. The dark 

 central ring of A is formed, because the lights of maximum intensity 

 throufdi the air film are tlie very ones which are of nn'nimum in- 

 tensity through the mica film. The re;ison why tlie ))ands are cur\ ed, 

 is obvious. If we form a white central spot by an approach of A 

 tow.ard the centre, the straight bands coincide with curved bands, so 

 that lights wliich are as a, mininumi after interferrence through the 

 îdr film, are still minimum after the interferrence through the mica. 

 Hence no change is produced b}' the mica film. After a few colored 

 ring's, whose fn'mations can be readily understood after the above 

 explanations of the formations of dnvk and bright rings, there is a 

 space of uniform illumination. And then a second group that may 

 be called the group lî, very similar to A is seen. Here again in the 

 middle dark ring, the liglits of maximum intensities through the air 

 film are mininumi by the interferrence through the mica. If a 

 central dark spot Ix' formed of the dark ring and its spectrum 

 examined, we again see a series of straiglit and cur\ed bands, but this 

 time tlie munljer of curved bands are twice as many as straight ones. 

 And one of the straight ones coincides Avith one of the curved ones 

 in the middle part of the latter. If a central wliite spot formed by 

 Avhite rings of 15 group be examined, the two curved ones fall neither 

 on the curNcd dark bands nor on the part just mid-way between 

 two bands, corresponding to the light of maximum intensity, but 

 between the two, so that the light of maximum intensity passes 

 through the mica. AMiate^'er be the order of the group, in the middle 



