FIG. 83.-Ratio of evaporation from water surface in field (upper curve) and forest (lower curve) to precipitation (top line).

I. THE WORK IN TIMBER PHYSICS IN THE DIVISION OF

FORESTRY.

BY FILIBERT ROTH,

Late Assistant in the Division of Forestry.

HISTORICAL.

As in the case of other materials, exact investigation of the properties of wood did not begin until the latter part of the eighteenth and the beginning of the nineteenth century, when Girard Buffon and Duhamel du Monceau in France, and Peter Barlow, the nestor of engineering in England, laid the foundation for this inquiry by devising suitable methods and working out correct formula for the computation of the results. As might be expected, the results of this pioneer work, particularly that of the French investigators, were often contradictory, and have to-day little more than historical value.

Subsequently our knowledge of wood in general, and that of European species in particular, was increased by a number of experimenters. Among these, Chevandier and Wertheim in France, and Nördlinger in Germany, stand out conspicuous. Unfortunately, their apparatus was crude and, in the case of the French workers, the series was too small to satisfy so complicated a problem, while Nördlinger was obliged to content himself with small and few specimens, owing to a want of proper equipment.

In England considerable money was expended from time to time both by Government and private enterprise, but the eagerness of making the matter as practicable as possible led, unfortunately, to much testing of large sizes and to the employment of insufficient (because unsystematic) methods, so that such extreme experiments as those of Fowke and others have really neither furthered science nor helped the practice. In this country the engineering world for a long time relied largely on the results of European testing, and the wood consumers in general depended on a meager accumulation of experience and crude observation concerning most of the fine array of valuable and abundant kinds of timber offered in our markets.

Ignorance and prejudice had their way. Chestnut oak was pronounced unfit for railway ties, and thus millions of logs were left rotting in the woods, though this prejudice had not a single fair trial to support it. Bled" longleaf, or Georgia pine, was considered weaker and less durable, millers and dealers were obliged to misrepresent their goods, causing unnecessary loss and litigation, and yet there existed not a single record of a properly conducted experiment to substantiate these views. Gum was of no value, Southern oak was publicly proclaimed as unfit for carriage builders, and the views as to the usefulness of different timbers were almost as numerous as the men expounding them.

The engineering world was the first to realize this deficiency, and men like Hatfield, Lanza, Thurston, and others attempted to replace the few antiquated and unreliable tables of older textbooks by the results performed on American woods and with modern appliances.

In addition to these efforts of engineers, Sharples, under Sargent's direction, in his great work for the Tenth Census of 1880, subjected samples of all our timber trees to mechanical tests, but, since in these tests only a few select pieces represented each species, the engineering world never ventured to use the results. As regards the rest of the wood testing in our country, it may be said that it generally possessed two serious defects: (1) the wood was not properly chosen, and (2) the methods of testing were defective, especially with respect to the various states of seasoning, wood being tested in almost every state from green to dry, without distinction. This is the more

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remarkable since the important influence of moisture was recognized and emphasized by both French and German experimenters more than forty years ago.'

These facts were fully appreciated by the engineers of our country, as is well shown by the numerous, often emphatic, approvals and recommendations of the timber-physics work undertaken by the Division of Forestry, and by the eagerness with which wood consumers generally seized on all information of this kind as fast as the Division of Forestry could supply the same.

SOUTHERN AND NORTHERN OAK.

Though fully planned before, the work in timber physics was really begun in order to decide an important controversy as to the relative value of Southern and Northern grown oak.

A representative committee of the Carriage Builders' Association had publicly declared that this important industry could not depend upon the supplies of Southern timber, as the oak grown in the South lacked the necessary qualities demanded in carriage construction. Without experiment this statement could be little better than a guess, and was doubly unwarranted, since it condemned an enormous amount of material, and one produced under a great variety of conditions and by at least a dozen different species of trees, involving, therefore, a complexity of problems difficult enough for the careful investigator, and entirely beyond the few unsystematic observations of the members of a committee on a flying trip through one of the greatest timber regions of the world. A number of samples were at once collected (part of them supplied by the carriage builders' committee) and the fallacy of the broad statement mentioned was fully demonstrated by a short series of tests and a more extensive study into structure and weight of these materials. From these tests it appears that pieces of white oak from Arkansas excelled well-selected pieces from Connecticut both in stiffness and end wise compression (the two most important forms of resistance). Results of tests on Northern and Southern white oak made in Washington University Laboratory, St. Louis, Mo., by Prof. J. B. Johnson, 1889.