[Illustration: Formula No. 8, A. C.] [Illustration: Formula No. 9, A. C.] [Illustration: Formula No. 10, A. C.] [Illustration: Formula No. 11, A. C.] [Illustration: Formula No. 12, A. C.] [Illustration: Formula No. 13, A. C.] [Illustration: Formula No. 14, A. C.] [Illustration: Formula No. 15, A. C.] [Illustration: Formula No. 16, A. C.] [Illustration: Formula No. 17, A. C.] [Illustration: Formula No. 18, A. C.] [Illustration: Formula No. 19, A. C.] [Illustration: Formula No. 20, A. C.] [Illustration: Formula No. 33, A. C.] [Illustration: Formula No. 34, A. C.] [Illustration: Formula No. 35, A. C.] [Illustration: Formula No. 36, A. C.] [Illustration: Formula No. 37, A. C.] [Illustration: Formula No. 38, A. C.] [Illustration: Formula No. 39, A. C.] [Illustration: Formula No. 40, A. C.] [Illustration: Formula No. 45, A. C.] [Illustration: Formula No. 46, A. C.] [Illustration: Formula No. 47, A. C.] =Making Photomicrographs.= The photomicrographs which are herewith shown were made in the following manner: A part of a panel was placed upon the stage of the microscope and held firmly in place with clips. By varying the adjustment and carefully running over the field the condition of the surface was readily given, using the same eye-piece and objective throughout the tests, and obtaining a magnification of thirty-three. Great care was exercised to secure an average field showing the general and typical appearance of every panel. Little difficulty was experienced in so doing, as the laboratory panels gave very representative surfaces of the large panels on the fence. The instrument was then inclined horizontally and the eye-piece was fitted into the camera nose. In the back of the bellows of the camera was placed the ground glass for focusing. To secure illumination the light from an electric arc lamp was reflected from a mirror directly upon the painted surface of the panel, which in turn was reflected through the camera on to the ground glass. The plate-holder was then put in position and six-second exposures were made, afterward developing and printing. =Checking and Cracking.= What was termed "fine matt checking" at the First Annual Inspection was not visible at the time to certain members of the Inspection Committee, but it is an established fact that the checking was an existing condition, as the photomicrographs have shown. This checking has a very peculiar characteristic in that the lines are very narrow and hair-like, being somewhat interlaced and peculiarly forked. That this hair matt checking is a preliminary condition which afterwards develops into matt checking and into marked or heavy checking seems to be indicated.