Show MEASURES 1 OTH OF INCH new apparatus of english invention that W will M determine extremely minute distances the extreme delicacy of icy measurement is shown by an apparatus of 0 english invention for or comparing official standards of length its action depends upon the interference of light waves causing shadow bands the width ot of which Is ha halt f the tb wave length ot of the light employed the red radiation from hydrogen or cadmium Is used and its wave ave length Is say the 50 lomoth of an inch thai machine carries two one of which 1 Is attached to one of the glass plates reflecting the light and producing the interference bands first the recognized standard rod say the imperial standard yard Is placed under the two microscopes and one of its terminal marks Is brought under the spider lines of each then the rod to be tested is substituted and one of its terminals is accurately adjusted it if it varies from the length of the standard the other microscope carrying the ref must be shifted until coincidence Is obtained the number of bands that move past during the shifting shit ting multiplied by the halt half wavelengths wave lengths of the light gives uie the difference in length of the rods scientific american |