This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ...into the telescope and was brought to a focus on the ground glass screen fastened to the end of the mirror. The point of light could be moved in a vertical direction on the ground glass screen by adjusting the fixed mirror by means of a thumb screw about its horizontal axis. To adjust for a run, the rotor was turned over until the quadrant line 1 on the rotor was in a horizontal plane as determined by a trammel. The mirrors were adjusted until the point of light was at the intersection of the vertical line and horizontal line 1 on the ground glass screen. Then horizontal lines were drawn lor 2, 3 and 4 and finally 1 again, as shown in Fig. 108. When the motor was started the beam of light traveled up and down the vertical line on the screen and as the speed increased this becomes a continuous bright line. As soon as vibration started the mirror was oscillated and the beam of light followed a curved path depending on the displacement of the bearing from vibration. The curvature of this path is a measure of the dynamic unbalance of the rotor. The rotor speed was increased to its maximum and the critical speed (which shows the greatest displacement of the line) was noted. The rotor was brought again to this critical speed and the path of the team was drawn on the ground glass screen, as in Fig. 108. This curve indicated maximum displacement along the radial line 3. However in practice it has been found that the heavy spot is always in advance of the maximum displacement on the screen. The rotor was then run in the opposite direction at the same critical speed and Fig. 109 was obtained. ThiB showed that the heavy spot was in advance of radial line 1. A study of the diagrams indicates the probable location at 4. Hence a weight of a few ounces was added near the ...