the ending of each year's growth, which is usually the best measuring-point. In good reproductions the measures are satisfactory, different observers agreeing within 0.1 to 0.2 mm. In others, however, there is much chance for judgment in selecting the measuring-point, and observers differ 0.3 to 0.5 mm. Nevertheless it is easy to judge of the relative sizes of rings and the only injurious effect is to reduce variations.
The cross-identification was very satisfactory, with practically no doubtful cases and only a few which required careful study. It is not likely that there is a single error in identity throughout the 17 sections in this group. Two other trees, one cut in 1909 and the other of
Fig. 11.—Oregon group. Curve No. 1, actual tree-growth; No. 2, tree-growth departures, smoothed; No. 3, sunspot numbers displaced 2 years to left.
unknown date, but probably cut in 1902, were not included. They showed special characteristics, such as an evident injury in 1861-62, affecting the 1862 ring and several others following it. They show also small growth in 1886, and even in 1887 and 1888 following the minimum growth of 1884 and 1885 prominent in the large group. The tree (cut probably in 1902) shows a minute growth in the years 1779 to 1783 inclusive, evidently the result of injury. These two sections are full of character and may prove valuable.
Five other rubbings similar to the group of 17 were discarded because defective in some parts. The attempt to trace the lost lines with a pencil-mark gave no help. One of the 17 was defective since