temper. The effect of temperature on the magnetism of steel was similarly treated and rules were given for the construction of magnets of exceptional degrees of magnetic permanence. In a great variety of magnetic instruments it is essential that the magnets used shall have the greatest possible power of resisting the effects of wear and tear, as well as of atmospheric agencies, and that the result shall be secured at the least possible sacrifice in the amount of magnetization. Thus the practical construction of exceptionally permanent, highly magnetized magnets is an outcome of this research.

The authors also discussed a scheme for the physical classification of the iron-carbon products. This classification is based on the important observation that the difference between the electrical constants for the soft state and the hard state of a given iron-carbide increases with the number of states of mechanical hardness in which the sample is capable of existing. Thus, for wrought iron, which can not be tempered, the difference in question is nearly zero, and for cast iron it is smaller than for steel. This difference, however, would not necessarily imply the changes of mechanical properties which are observed in passing from iron through steel into cast iron, even in the soft states; and the electrical expression for this difference is also a continuous increase of the constants. Hence the ratios of the electrical constants for the hard and the soft states of any given iron carbide were selected as a basis of classification. Experiments then proved that on passing without break of continuity from pure iron to cast iron a unique iron carbide is always encountered in which the ratio of the electrical constants is a maximum. This singular iron carbide is characterized by the notable property of existing in the greatest possible number of mechanical states of hardness. The metal thus definable with almost mathematical precision is steel.

In a series of subsequent researches Dr. Barus and Dr. Strouhal developed the practical side of the inquiry with much greater fullness.' Thus the density of steel in its relation to

1Bull, No. 27 (pp. 30–61, 1886), Bull. No. 35 (pp. 1–62, 1886), and Bull, No. 42 (pp. 98-131).

14 GEOL—10

White, Prof. H. S. Williams, of Cornell University, and Mr. C.
D. Walcott.

These essays summarize our present knowledge of the groups of rocks of which they treat and outline the special investigations which are necessary to solve the various problems bearing upon the geology of the country. An essay on the value of paleobotany in correlation is in course of preparation by Mr. Lester F. Ward.

COLLECTIONS.

ORGANIZATION AND METHOD.

Collections of fossils and rocks obtained from typical localities of determined sections of strata are the most important books of the paleontologist and geologist. Such collections constitute a permanent record of work done; and under the organic law of the Geological Survey they are to be deposited in the National Museum when no longer needed for investigations in progress.

Early in the history of the Survey an arrangement was made with the National Museum under which the collections of fossils were placed in the charge of certain members of the Geological Survey, who were appointed honorary curators of the National Museum. In return for the supervisory work of these curators, the National Museum furnished laboratories and the necessary facilities for work. By this cooperation all material was brought under the charge of specialists, and work was systematically carried on both for the Geological Survey and for the National Museum. Immense collections have been thus transferred to the National Museum through the work of the Geological Survey; but both these institutions have been unable for a number of years to provide room for the proper exhibition of material, or necessary laboratory room for work upon the study series. Owing to this lack of room the work of several divisions of the paleontologic branch has been carried on in laboratories outside the city of Washington.

COLLECTIONS NOT YET PLACED IN THE NATIONAL MUSEUM.

The collections in charge of Prof. Henry S. Williams are in the museum building of Cornell University. They are ar

ranged in two rooms in trays and cases, and so separated from the collections of the university that they may be readily distinguished, even if the specimens should be mixed in trays for the purpose of study or comparison, a distinct green label with its record number marking those belonging to the Survey from those belonging to the university or elsewhere. The record numbers placed upon each green label were assigned to Prof. Williams from the Geological Survey and National Museum catalogues. Prof. Williams has prepared a card catalogue of all the numbers that he has used, giving the record of locality, geological formation, collector, date of collecting, and any other information relating to the geographic and geologic position of the specimens. A copy of this card catalogue is being prepared, to be filed with the records of the Geological Survey. There are now in Prof. Williams's charge five hundred drawers of fossils, the drawers averaging in size 2 feet by 1 foot 6 inches and 3 to 4 inches deep. There are also 13 boxes of duplicates packed ready for shipment to the Survey whenever they may be required.'

The collections in charge of Prof. Alpheus Hyatt, at Cambridge, Massachusetts, are arranged in drawers in a room entirely devoted to their keeping in his private house. The collections belonging to institutions or individuals, which are used in the course of his study, are kept in another room on the floor above. The collections are in good order. The method of recording the specimens is the same as that used by several of the paleontologists of the Survey in Washington, and includes the use of a round green or yellow label, which is numbered and fastened to the specimen to indicate geographic location and geologic formation when the latter is known. The material is contained in about fifty drawers, and includes the collections made since 1888. A copy of Prof. Hyatt's record book will be filed with the Survey. The collections in charge of Prof. S. H. Scudder are kept in special cases in the laboratory building back of his dwelling house. The specimens are

Since the preceding was reported Prof. Williams has sent the duplicate collections to Washington and removed the study series to Yale College, New Haven, where he is now located.

temper and internal physical structure was discussed in detail. Moreover, the oxide films by which the temper of steel is usually estimated were made the subjects of direct measurement, and their growth was interpreted as a phenomenon of solid diffusion. Finally, an independent line of evidence was brought to bear on the question of temper by examining the singular strain existing in suddenly cooled glass. The distribution of density which characterizes this strain, as well as its relations to temperature, were accurately determined, and the results were corroborated by aid of the polariscope.

Having in this way obtained some definite information concerning temper and the laws of its variation, it was found that the study of viscosity could be entered upon with advantage. This part of the work was carried out by Dr. Barus.1 The researches begin with a study of the effect of temper on torsional viscosity, and among other results the extraordinary fact was revealed that steel is more viscous in proportion as it is harder and less viscous in proportion as it is softer; in other words, steel so hard that it easily scratches glass is nearer the liquid state than is soft and malleable steel. It follows that any theory designed to account for viscosity must suggest independent mechanisms for viscosity and for hardness. At about 200° C., however, steel is less viscous and much more susceptible to changes of temperature in proportion as it is harder, so long as a certain limiting value of stress is not exceeded. Beyond this, steel is less viscous and more susceptible to temperature in proportion as it is softer, thus indicating a complete. inversion of the strength of the viscous resistances encountered.

With these data in hand the subject was ripe for theoretic treatment, and some method of coordinating the mass of facts seemed essential. Many of the phenomena obtained had already been found to be interpretable by a method similar to Clausius's theory of electrolysis, and hence in preference to other theories Maxwell's views on viscosity were made the basis of discussion. All the data were therefore marshaled with reference to Maxwell's views, and the test to which the theory was subjected was as satisfactory as it was severe, the effect of

1 Bull. No. 73 (pp. 1-139, 1891) and Bull. No. 94 (pp. 1-138, 1892).

each agency (heat, stress, magnetism, time, etc.) being considered in detail. The work showed it to be necessary to distinguish two species of molecular break-up, viz, that in which the molecules pass from configurations of less to configurations of greater stability, apparently without loss of their individuality, and that in which the transfer is accompanied by a disintegration of the molecules. The last of these cases is exemplified by the changes of temper in steel, whether brought about by change of temperature or by time. Thus glass-hard steel is always spontaneously softening, even at ordinary temperatures. This is proved by the changes of the electric constants of steel in the lapse of years. The other case of configurational break-up, namely, that in which the configurations are of a physical character, is apparently the more common. Examples properly belonging here were obtained in abundance by subjecting metals to intense tensile, compressional, flexural, torsional, and other strains, the presence of each of which in the metal was accompanied by marked decrease of viscosity. In spite of the fact, therefore, that the hardness and tensile strength of steel are notably increased by stresses or strains, the metal itself is none the less brought nearer the liquid state, because the strains introduce a greater number of instabilities than were present before stress was applied. On the other hand, slight mechanical strains (twisting, for instance) increase the viscosity, because the instability thereby broken down exceed the number evoked. This effect is therefore analogous to thermal annealing, which is always accompanied by increased viscosity.

At this stage of progress much time was spent in the endeavor to obtain concrete knowledge of the mechanism of viscosity. Thus the effect of mechanical strain on the carburation of steel and on the rate of solution of the metal was considered. The hydroelectric effect of permanent changes of molecular arrangement was measured, and also the amount of energy potentialized by such strains. The most interesting results obtained came from a study of the electrical resistance of glass under stress at temperatures above 100° C. Here stress produced a greater decrease of resistance than could be accounted for by change of dimensions, and