��THE POPULAR SCIENCE MONTHLY.
��"W. A. Rogers, its builder, witli which a millionth of an inch can be easily meas- ured, and with careful adjustment even one twenty-millionth of an inch. In ])rinfiple the aiiparatus is an ai)plication of Prof. A. A. Michelson's interferential refraotometer, the interference of light- waves from mirrors attached to a standard and to a compared metallic bar enabling the observer to determine minute movements with a precision hitherto impossible.
An inquiry into the properties of paraldehyde and metaldehyde by Profs. W. R. Orndorflf and John White illus- trated the inferences whereby the chem- ist is able to body forth the respective positions in a molecule of the atoms which compose it. In the Anthropo- logical Section the songs of sequence of the Navajoes were rendered by a phono- graph, an instrument which promises to be as indispensable as the camera to the serious traveler. A discussion of the most animated kind took place in this section between Rev. G. F. Wright and Mr. W J McGee on certain evidences adduced by the former of preglacial man, Mr. McGee maintaining that the evidence was merely probable and not conclusive.
OUR NEW INDEX.
Half a century ago science was an affair of a ^ew individuals, and a labora- tory of any kind was to most people only a curiosity. The man who devot- ed himself to the study of Nature was looked upon as a visionary having nei- ther place nor function among the con- tributors to human welfare; scientific methods in the arts were rarely heard of; natural knowledge had no part or place in education; and, besides an oc- casional learned treatise, two or three technical periodicals met all the needs of scientific publication.
But all this has now been changed. The last half of the nineteenth century will long be memorable as the period during which science achieved a promi-
��nent if not a leading place in nearly every department of human activity. The wonderful advance of discovery, closely followed as it has been by numerous practical applications, has wrought a revolution in many fields, until in the arts, in commerce, in edu- cation, and even in the professions, science may justly claim to exercise a controlling influence.
W^ith all this there has come an enor- mous increase in the volume of scientific literature. Scores of scientific periodi- cals are engaged in the work of dissemi- nating the results of investigation and books by the hundred are published every year in which the methods and conclusions of science are given more permanent record. The accuumlation of material from this ceaseless and ever- increasing activity is already so great that ready means of access to it be- comes an urgent need of the hour.
But it is only with a subdivision of this great body of knowledge that we are here specially concerned. In the early days of the scientific awakening just alluded to, it was only natural that the results obtained by workers in sci- ence should for the most part remain the possession of the student and in- vestigator. That science, however, had a message for the people was not long in being perceived. Side by side with its many important industrial applica- tions there had grown up a vast body of scientific knowledge only needing suitable interpretation to make it avail- able for the masses. Under the stimu- lus supplied by a few enthusiastic public teachers there gradually arose a demand for this new kind of knowledge that would brook no refusal. In obedience to this desire of the public we have seen issuing from the press during the last twenty-five or thirty years a steadi- ly growing stream of popular scientific literature embodying the ablest thought of the time, and much of it the direct product of our most distinguished scien- tific men.