Page:Popular Science Monthly Volume 38.djvu/575

Rh of time and movements of the heavenly bodies," the location of Vinland might be a matter of doubt; but it is fixed not only by their description of the coast and character of the country, but by the account of Leif and his comrades, that "on the shortest day the sun was in the sky between Eyktarstad and Dagmalastad," periods corresponding to 4.30  and half-past 7, making the latitude 41· 43' 10", nearly that of Mount Hope Bay. Ancient vessels that have been exhumed in Denmark, as well as measurements found in the Sagas, prove that the ships of the Northmen were able to bear them across the Atlantic. That no enduring structure marks their occupation of New England is not astonishing; according to the story of their sojourn, they lived in wooden booths.

The literature and general knowledge of the Icelanders were much in advance of the rest of Europe during the twelfth century, so that it is altogether credible that they wrote the Sagas and performed the voyages recorded. A corroboration of the Icelandic writings is also found in early English annals, which contain statements and dates that exactly agree. The manuscript from which the Sagas are taken is the Codex Flatöensis, "a work that was finished in 1395 at the latest, . . . and now preserved in the archives of Copenhagen."

The latter part of Dr. De Costa's work is devoted to translations from these writings, relative to the pre-Columbian voyages. Extracts are given from the Landanama,'the doomsday-book of Iceland; from the Sagas of Eric, composed in Greenland; and from the Saga of Thorfinn, of Icelandic origin. Following these are minor narratives taken from the Eyrbyggia Saga, and two geographical fragments that mention Vinland. Although the volume possesses an index, it has the unusual distinction of being a book without chapters.

author of this book does not discuss purely inorganic dust of any sort, not even the specially injurious kinds resulting from processes of manufacture, but in a simple and attractive way tells of the common dust that is dangerous—that which contains micro-organisms hurtful to man. He describes the classes of germs that can be identified, and explains how biological analyses of the air are made by the "filtration" and the easier "plate method." Comparison of averages obtained in various cities and in different localities in New York show that the number of bacteria in a given volume of air varies chiefly according to condition, the process of street-cleaning summoning the greatest number of germs, 5,810 to a disk 3inches in diameter. Indoor air is, however, the main subject of investigation, and experiments prove that ventilation which completely changes the atmosphere three times an hour will not appreciably affect the number of bacteria in an apartment, as the intruders cling obstinately to the carpets and upholstery. Only violent currents of air dislodge these, and the sweeping and cleansing which result in removing, not redistributing the dust. Ordinarily we are liable to take in with every twenty breaths from eleven to eight hundred and seventy-six organisms.

Among the disease-breeding bacteria Dr. Prudden selects for study the one numbering most victims, the Bacillus tuberculosis. He points out that prolonged drying does not kill it; that it does not exist in the air exhaled from consumptive lungs, but in the sputa that is ignorantly allowed to become part of the dust. It results that "the way to most efficiently stop this distinctly preventable disease is to see that the sputum of consumptives is properly disposed of."

One of the most instructive chapters is that in which the action of the cilia, of the lymph-filters, and of the wandering white cells, is described. A number of illustrations and an index accompany the book, which is published in uniform style with The Story of the Bacteria, by the same author.

of lectures, delivered at the Academy of Natural Sciences, in Philadelphia, during the early months of 1890, forms the basis of this book. In the first two lectures are given respectively the physical and the mental characteristics of races, upon which ethnography is based. The third