Page:Popular Science Monthly Volume 20.djvu/880

858 parasitic bodies were found in the blood only at certain times, a little before and at the moment of the accession of the fever; and they rapidly disappeared under the influence of a quinine treatment. The addition of a minute quantity of a dilute solution of sulphate of quinine to a drop of blood sufficed to destroy the organisms. Mr. Laverau believes that the absence of the organisms in most of the cases (only twelve in the whole one hundred and ninety-two) in which he failed to find them was due to the patients having undergone a course of treatment with quinine.

The Freezing of a Salt Lake.—Dr. Woeikoff has published the results of some observations which were made at his suggestion into the conditions of freezing and thawing of a salt lake near Orenburg, Russia. The lake has a surface of 473 square metres and is about five feet deep. Its water contains sixteen per cent of salt, and the mud of its bottom is rich in sulphuretted hydrogen. During January, 1879, except for one day, when the temperature was barely above the freezing-point, the thermometer in the air ranged from -6·3° to -28·2° centigrade, while the temperature of the water at the surface was from -3·4° to -13° C., and at the bottom from -3·8° to -12·8° C. On the 27th of December, when the temperature of the air was as low as -21° C, the lake was covered with a viscous ice, which soon began to thaw, however, when the temperature of the air rose to -6° C., and the temperature of the water was as low as -7·8° C. By the 3d of January all the ice had disappeared, but the temperature of the water was still 7·2° C. below the freezing-point, or about 19° Fahr. On January 11th, the temperature of the air being -22° C, and that of the water being -9·8° C. at the surface and -5·6° at the bottom, the lake began again to be covered with viscous ice, and soon froze, the ice reaching a thickness of about six inches in ten days. But the remainder of the water was still unfrozen, notwithstanding that its temperature decreased to -10° C. on January 17th, and even to -12·8° C. on January 30th. Never before, says Dr. Woeikoff, were temperatures below -4° C. or 24·8° Fahr. observed in saline solutions outside of laboratories, while here were temperatures of -13° C, or 8·6° Fahr., observed in a salt lake. However, former experiments, especially those of M. Zöppiitz, have proved that there is no diffusion of salt before congelation; it seems that in this lake (Kupalnoze) there is such a diffusion of salt toward the lower stratum of water, even before the freezing begins, otherwise it would be difficult to explain how colder water might remain on the surface, were it not for the greater amount of salt in the lower strata. It has always' been difficult to explain how ice is formed on the surface of oceans while the temperature of maximum density is lower than that of congelation, and the observations on this lake were instituted in the hope that they might throw light upon the subject. The lake, however, contains too much salt to afford a sure standard of comparison with oceanic water.

A Collection of Quaint Scientific Instruments.—The Royal Mathematical and Physical Museum, in Dresden, Saxony, was founded by Prince Augustus I in the sixteenth century, and has grown into an extensive collection of articles illustrating the condition of science at particular periods, and its progress. "According to Adam Ries," a German expression to denote that any fact is mathematically exact, refers to the mathematician, Adam Ries, who in 1550 published a little book on reckoning with counters and with the Arabic numerals. His counters, and the hand-circles, staffs, and various devices with which people made their calculations before the Arabic numerals came into general use, are shown here. Another curious instrument, of the eighteenth century, is a proportion staff "for the mechanical extraction of the square and cube roots, and the proportioning and calculation of geometrical figures." Among the optical instruments is the famous burning mirror of Walter von Tschirnhausen, of which the "Acta Erudita" from 1687 to 1697 says, "He has with this glass set fire to wet wood in an instant, boiled water in a small vessel, melted lead, bored through iron plates, changed brick and stone to glass." Tschirnhausen performed the first experiments on solubility of the earths with this instrument.