ACOUSTICS AND GRAVITATION. 73 



in the direction r are drawn out in the direction s, nearly normal to r. Thus if 

 the fringes are very short, they will be displayed as fringe bands, as heretofore. 

 So far, therefore, the conditions are met. 



If, however, we return to figure 97, it appears that if the fringe ai has been 

 carried by the rotation of mirror to the position 02, the objective will have 

 simultaneously carried it to 62 etc. In other words, the fringe i will always 

 remain on the line EE', regardless of the retardation of light; i. e., the line EE' 

 will not move in the directions dd' as in the case of the independent revolving 

 mirror and telescope. The effect of the revolving mirror has simply been 

 compensated. 



Nevertheless, this method of approaching the problem is well worth while, 

 since it affords opportunities for correcting the details of the experiment. 

 Strong fringes were produced without much difficulty and viewed through the 

 telescope EP in the s'r' position. But in spite of many trials, it has thus far 

 been impossible to secure a sufficiently rigid and independent mounting of the 

 disk tt' and revolving mirror to hold the fringes in the field during rotations of 

 5 to 10 turns per second. 



