456 M. E. Wilde on the Untenableness of 





contact has taken place, and that the distance between the 

 glasses is already =0 when the shape of the rings has begun 

 thus to alter, inasmuch as this alteration manifestly intimates 

 an actual pressure of the glasses. Then, however, the first 

 bright ring must appear as the uninterrupted continuation of 

 the bright central patch, because the first dark ring is not 

 formed until for cos r = cos 0°= 1 the depth d of the layer of air 



is — , the difference of the paths of the interfering rays (taking 



into account the journey forward and back through the air- 

 layer and the reversion of the vibration) being at this place 



= 2 — + — = —, and the light consequently destroyed. When 



4? Z £ 



this is the case, we have with reflected light, 



the maxima for 



, A, 3\ 5\ 7X 



d—0 and , = - , —- , = - , 



4 cos r 4 cos r 4 cos r 4 cos r 



and the minima for 



c l\ 4A 6X _ 8\ 



4 cos r 4 cos r 9 4 cos r 9 4 cos r 



With transmitted light, on the contrary, 



the maxima for 



_2A_ 4A, 6\ S\ 



4 cos r 9 4 cos r* ~~ 4 cos r 9 ~~ 4 cos r 



and the minima for 



, „ V X 3X 5X 7X 

 d=0 and , =- , =-; , =- , 



4 cos r 4 cos r 4 cos r 4 cos r 



from which it follows, that with reflected light the radii of the 



successive bright rings are in the ratio of \/l : \/3: \/5 , 



and those of the dark rings in the ratio of \/2: V^\ ^6...... 



With transmitted light, however, the radii of the bright rings 

 are in the ratio ^2: v^4 : \/6..., and of the dark rings in the 

 ratio \/l : VS : \/5...; the middle of the system, up to the 



points where the layer of air reaches a depth ofd= — , appear- 



ing at the same time in maximum with reflected light, and 

 in minimum with transmitted light. 



The measurements I have made with the gyreidometer, in 

 which were placed a plane glass and a convex glass of 360 

 inches Eng. radius, are my security against error here. When 

 using reflected light, the glasses were pressed together until 

 the circular form of the rings began to alter, the middle of 



