MORLEY AND MILLER. — THE FITZGERALD-LORENTZ EFFECT. 325 



diameter; each pair of tubes is joined together in a vertical truss, as 

 shown in Plate 1. Against the farther end of these rods there rest the 

 frames which hold the two sets of mirrors, I and II, Figure 1. Each of 

 the latter frames is freely suspended by two thin steel ribbons and is held 

 firmly against the pine rods, and through these against one of the two 

 fixed mirror holders ; the pressure is applied by means of adjustable 

 spiral springs. Thus the distance between the opposite systems of 

 mirrors depends upon the pine rods oidy. This construction permits the 

 convenient substitution of distance rods of other material, so that experi- 

 ments might be easily made to test the theory that the dimensions of 

 different materials are differently affected by motion of translation 

 through the ether. The diagonal mirrors are carried by adjustable 

 supports bolted to the steel frame near its centre. 



The observing telescope of an inch and a half aperture with a mag- 

 nifying power of thirty-five is attached to a support bolted to the steel 

 frame. The acetylene lamp and the four-inch condensing lens stand on 

 a wooden shelf as far as convenient from the mirrors, which are pro- 

 tected by asbestos screens with air spaces. The whole path of light 

 through the apparatus is enclosed by a wooden cover made of pine seven 

 eighths of an inch thick, having doors and glass windows where these are 

 required. The observer's eyes are protected from extraneous light by a 

 dark cloth. 



The entire apparatus, weighing about nineteen hundred pounds, rests 

 upon a circular wooden platform about five feet in diameter. An annu- 

 lar projection on the under side of the platform is immersed in mercury 

 of such depth as to float the platform and the apparatus. The mercury 

 is contained in an annular cast-iron trough of such dimensions as to leave 

 a clearance of about half an inch between the iron and the wooden float. 

 A small pin at the centre of the iron trough enters a socket in the wooden 

 float, so as to keep the float from touching the sides of the trough. 



Plate 1 shows the steel framework and float, together with the 

 trusses which are to support the distance pieces. The mirror frames 

 and the telescope are in position, but lamp and lens are not in position. 

 Plate 2 shows the apparatus as it appeared at the time of the observa- 

 tions. 



With this apparatus, fringes adjusted on a certain Monday remained 

 in adjustment throughout the whole of the week during which our obser- 

 vations continued. Observations were made in precisely the same manner 

 as with the previous apparatus. 



We obtained 2G0 complete observations, consisting each of readings at 



