December 21, 1893J 



NATURE 



181 



•while the level of the river was lower near Hamburg this year. 

 It appears from the facts brought forward, that meteorolgical 

 •conditions were in no way connected with the outbreak or 

 spread of the disease, and that the cause must be attributed 

 entirely to the accidental contamination of the water of the 

 Elbe. 



An abstract on the " Occurrence of Amber in Russia," by 

 Fr. Th. Koppen, is published in Petermann s Mitteiliw gen, 

 November 1893, pp. 249-253. The original paper by the same 

 author appeared in a Russian publication. Amber is found on 

 the Baltic shores, the south coast of the Gulf of Riga, and in 

 turf-moors or ancient gulfs of Kurland, embedded below thin 

 beds of turf or sea-sand. Farther north, it occurs on the 

 shores of the Oesel Island, and even in South Finland. The 

 Polish localities along the river Narew are supposed to have 

 been those referred to by Pliny. The most extensive occurrence 

 is in the western provinces of Russia, and in different places on 

 the banks of the Dneiper. From these facts, the "amber- 

 formation " may be said to occur in Western Russia, from the 

 Baltic to the Black Sea. A recent paper, written by N. Soko- 

 low, shows that the lower tertiary deposits of Southern Russia 

 extend also throughout this area. Sporadic appearances of 

 amber occur in the southern parts of Bessarabia in brown-coal 

 strata ; they are possibly associated with the amber found in 

 Roumania. Other Russian localities are the Arctic shores of 

 Russia and Siberia, and on the Sea of Okhotsk. A sketch- 

 map accompanies the text, showing the distribution of lower 

 tertiary deposits according to Sokolow, and the most important 

 occurrences of amber in Russia. 



Last week's number of Die Natur concludes a series of 

 eleven articles written by A. and S. Ortleb. The title of the 

 series is "Introduction to specimen-collecting, geological and 

 palseontological." The early chapters run rapidly through the 

 physical and geological history of the development of our earth, 

 and point out the significance of the fossils found in sedimentary 

 beds. A short, systematic description follows of the chief groups 

 in the plant and animal kingdoms. A few of the more inter- 

 esting genera are mentioned, illustrations are given along with 

 the text, and care is taken to bring out the particular epochs 

 and localities to which the fossil representatives belong. This 

 admirable contribution to popular scientific literature will supply 

 a want widely felt among amateur collectors in Germany. 



Mr. M. Carey Lea, who recently described a method of 

 transforming mechanical work into chemical action in the 

 Americati you7-nal of Science, hzshQcn continuing these inter- 

 esting researches, and gives a description of some further re- 

 markable results in the current number of the same journal. 

 Instead of an enormous simple pressure, he tried shearing stress, 

 and obtained more striking and apparent reactions than by the 

 former method. In one series of experiments he placed a small 

 quantity, a few decigrams, of a metallic salt in a mortar, spread 

 it into a thin uniform sheet over the bottom, and rotated the 

 pestle with the utmost force that could be exerted. Two of 

 three decigrams of chloroaurate of sodium left i 8 milligram or 

 metallic gold. Under the action of the pestle the yellow colour 

 of the salt gradually deepened to an olive shade. When water 

 was poured on, the undecomposed salt dissolved, leaving the 

 gold as a delicate purple powder. Half an hour's trituration 

 of half a gram of the salt resulted in the reduction of 9 "2 mgrms. 

 of gold. This reduction represented the conversion of about 

 500 gram- meters work into chemical energy. Since the re- 

 action is endothermic, there is no doubt that the energy was 

 derived from the mechanical power. That the reaction was not 

 produced by heat was proved by carrying on the operation 

 intermittently, when th^ reaction took place in the same way, 

 and also by the partial reduction of corrosive sublimate to 

 NO. 1260, VOL. 49] 



calomel by a similar operation. By heat, corrosive sublimate 

 sublimes unaltered. The same conclusion can be drawn from 

 other reactions. Salts of mercury, platinum, and silver gave 

 results analogous to those in the case of gold. In another series 

 of experiments Mr. Carey Lea imbued pure strong paper with 

 a solution of the substance, dried it thoroughly, and laid it upon 

 a piece of plate glass. Characters were then marked on it with 

 the rounded end of a glass rod, using as much pressure as pos- 

 sible without tearing the paper. Marks were thus immediately 

 obtained in the case of potassium ferricyanide, gold and plati- 

 num chlorides, mercuric oxide, and many silver salts. The 

 author accounts for the more immediate action of shearing stress 

 in effecting chemical changes by the increased vibration and 

 consequent shattering of the molecules, the action being analogous 

 to that brought about when a bow is drawn over a stretched cord. 



The third number of the Physical Review contains a paper, 

 by Alexander Macfarlane and G. W. Pierce, on the electric 

 strength of solid, liquid, and gaseous dielectrics. In the course 

 of a previous research Dr. Macfarlane had found that the 

 "electrical gradient " necessary to force a spark through a thin 

 stratum of dielectric diminishes as the thickness increases, when 

 air or other gas is the dielectric, but remains constant when 

 turpentine or other insulating liquid is the dielectric. Mr. Stein- 

 metz has shown that solid dielectrics, such as paraffined paper, 

 behave in the same way as the liquid dielectrics. In order to 

 obtain more trustworthy observations on these points, the 

 authors have compared the electrical gradient necessary to break 

 down different solid and liquid dielecttics with that required in 

 the case of air. For this purpose they employed two discharging 

 tables, each table supporting two parallel discs about 4 inches in 

 diameter, the connecting rods being joined to the poles of a 

 Holtz electrical machine, so as to form two alternative paths for 

 the discharge. One of the tables, that used for the air gap, 

 was provided with a micrometer by which the distance between 

 the plates could be measured. The sheets of dielectric were 

 placed between the other pair of discs, and the air gap enlarged 

 till a spark passed through the solid dielectric. The difference 

 of potential required was calculated from the length of the air 

 gap, using the results published by Macfarlane and Steinmeiz. 

 The equivalent thickness of air is not proportional to the thick- 

 ness of the solid or liquid, but increases more rapidly as the 

 stratum increases in thickness ; the difference of potential, how- 

 ever, required to break down a solid or liquid dielectric is pro- 

 portional to the thickness. Thus it appears that while thin 

 strata of solid or liquid dielectrics are equally strong whatever 

 the thickness, thin strata of gaseous dielectrics grow weaker as 

 the thickness increases. The authors consider that this difference 

 is not due to a surface phenomenon, but to the greater rarity of 

 the gas which allows discharge by convection to be more readily 

 set up. They find that for liquids, when the thickness is con- 

 siderable, convection currents are sometimes started, and that 

 in this case the discharge takes place at a lower difference <'f 

 potential. 



Wiedefuanii s Annalen for December contains a description 

 of a modified form of Thomson quadrant electrometer, which 

 has been employed by Herr F. Himstedt. The chief character- 

 istics are the employment of the form of needle which Lord 

 Kelvin uses in his multicellular voltrrieter, suspended by a quartz 

 fibre. The lower end of the row of needles carries an insulating 

 stem, to which are fixed two small magnets. These magnets are 

 placed with their axes vertical, so that the earth's magnetism 

 has no tendency to cause rotation of the needles, and are sur- 

 rounded by a thick copper shield, the induced currents in 

 which damp the oscillations of the needle. The fibre by which 

 the needle is suspended is covered with a thin coat of deposited 

 silver, so that it conducts, and thus allows the needle to be 



