100 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and of the apparatus G' (fig. 1!)) necessary for the decimal enlargement 

 of the measuring-scale ; and finally (4) of an inspection contrivance 

 V for the purpose of the proper adjustment of the light-source to be 

 measured. The weakening of the light emitted from the electric com- 

 parison light-source 0, and diffusely refracted through the three plates 

 v v v 2 , v 3 , set in the light-and-dust proof revolver D, is effected by the 

 fixed sector and rotating light-beam. The sector-measuring apparatus 

 consists of two equally large detached sectors operated by a handle g and 

 symmetrically arranged about a diameter ; they rotate over another pair 

 similarly arranged but of different size. Between the sectors are slits 

 forming the four arms of a cross. The opalescent glass plate v x (fig. 20), 

 regarded as self-luminous, is focused through the lens-combination L 1? L 2 , 

 sharply on to the wedge-shaped lens IK. The plane formed by the sectors 

 coincides with the focal plane of IK ; the eye-cap with the aperture A is 

 in the focus of the lens L, adjustable in the tube h. Thus at A the 

 sector-slits above referred to are sharply defined. For fuller explanation 

 the course of the rays must now be considered in a reversed direction, 

 i.e., originating from A. A sharp image of the eye-cap would now be 

 formed at a (rig. 20), but, on account of the refraction of wedge-lens 

 IK this image would be laterally displaced from the principal axis. If 

 rotation be imparted to the lenses IK, L 2 , L x , which are all set in a tube 

 rotatory about the principal axis, the image at a will describe a circular 

 path in a direction opposite to that of rotation. In its subsequent 

 course the light falls on the plate v v whose illumination would be in- 

 termittent on account of the slits between the sectors ; but this 

 illumination could be made uniform to the eye if sufficient velocity of 

 rotation were imparted, and the intensity of illumination would be pro- 

 portional to the aperture-angle of the sectors. The lenses L 1? L 2 , which 

 take part in the rotation, are continuously penetrated at the same 

 distance by the rays, and could not affect the proportionality. The 

 sector-adjustment can be read off on the circle S by means of the index N. 

 The graduation extends to 10, each main graduation being divided into 

 tenths. A small electric motor rotates R. 



The comparison-lamp O is electric incandescent, and is secured 

 within its chamber by strong clamps. This lamp-chamber is adjust- 

 able by push action in the axis of the instrument, the movement 

 being read off on the scale T, and the brightness can be regulated 

 within the limits of the current-intensity. Some adjustment of light- 

 intensity is also attained by passing the light through more than one 

 plate v (blue tinted if preferred) of the revolver D. To secure uni- 

 formity of diffusion through the revolver plates, the electric lamp, 

 approximately a point, should be mounted in an Ulbricht globe ; the 

 opal glass plate is then opposite a uniformly illuminated gypsum screen, 

 and transmission of the glow-threads is prevented. The position of the 

 rotatory upper structure H 2 in the main body H is governed by the 

 screw s 3 and the circular scale H. The glass strips k v h 2 , are for 

 attaining contrast, and can be applied to the Lummer-Brodhun cube LB 

 by small levers externally controlled. The light to be measured falls on 

 LB from /x or M through the tube h v fi being intended for measurement 

 of illumination and M for measurement of intensity. The lens LC not 

 only produces image-formation from (j. or M at the aperture A of the 



