Author Description

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. 1921 Excerpt:...normal places are shown in Figure 7. As we have anticipated, the images increase in size as their density increases; but there is a definite halt between wedge readings 32.5 and 45.0. Otherwise the function appears to be linear and similar for fainter and denser images. These results appear in Table X. Diameter vs. Spectrum. The color curve of the camera has not been studied, but we must suppose that the position of focus varies with the color of the star. What effect this has on the diameters may be learned by plotting the original diameter residuals after correction for density, against class of spectrum. Figure 8 exhibits the normal places for all the residuals so plotted. The result is surprising, in that no change in diameter due to color is evident between classes B5 and K0; beyond K0 the diameters decrease. The point for class N is due to a single image of the star B.D.-+76734, and this is unmistakably smaller than normal. The conclusion is that the color curve of the 5-inch camera is unusually flat. As the plates are exposed outside of focus, the smaller images for red stars indicate greater focal length for light of long wave length. Parkhurst1 finds for the 6-inch Zeiss lens a continuous though small variation of diameter with class of spectrum, resulting in a correction of nearly 0.1 magnitude from class K to class A. The Zeiss "UV" triplet of the Potsdam Observatory gives a correction several times greater2. Diameter vs. Reduction to Center. In order to coordinate J magnitudes resulting from measured densities of star images scattered over the plate, it is necessary to add an amount corresponding to loss of density as the image increases in size with distance from center. Other things being equal, the amount of the correction may be co...