METEOROLOGY. 



539 



fact that chemists have so long failed to recog- 

 nize anything other than ferric oxide as the 

 cause of the colors in these bricks, may prob- 

 ably be explained by the large number of 

 shades of color produced by iron in its vari- 

 ous stages of oxidation, by the presence of 

 manganese, and by the employment of mixed 

 clays containing the oxides of both cerium and 

 iron. 



It has long been known that the electrical 

 resistance of selenium is largely reduced under 

 the influence of light. Tellurium exhibits the 

 same property in a much less degree. In the 

 case of selenium the diminution has in some 

 instances been found to amount to a large pro- 

 portion of the entire resistance. In tellurium 

 the diminution is less than 1 per cent. In 

 1877, Dr. Richard Bornstein, of Heidelberg, at- 

 tempted to show that other metals, including 

 gold, silver, and platinum, possessed the same 

 property of having their resistance diminished 

 though in inferior degree. Siemens and Hause- 

 inann, of Berlin, afterward completed an inves- 

 tigation in which they were unable to detect 

 any action like that described by Bornstein. 

 Bornsteiu then made other experiments, in 

 which he believed he determined the property 

 to exist in silver. The next experiments to be 

 reported were those made by Arthur E. Bost- 

 wick in 1883. The results obtained by him 

 agreed with those of Siemens and Hausemann, 

 rather than with those of Bornstein, and led 

 him to indicate the conclusion " that, if light 

 causes any diminution in the electrical resist- 

 ance of metals, it probably does not exceed a 

 few thousandths of 1 per cent." 



Mr. Shelford Bidwell has been experiment- 

 ing on the changes produced by magnetization 

 in the length of rods of iron, steel, and nickel. 

 He has found that the length of an iron rod is 

 increased by magnetization up to a certain 

 critical value of the magnetizing force. If that 

 is passed, the elongation is diminished in pro- 

 portion as the magnetizing force increases. 

 The amount of the maximum elongation ap- 

 pears to vary inversely as the square root of 

 the diameter of the rod. In soft steel, mag- 

 netization produces elongation, and a tempo- 

 rary elongation, once produced, may be main- 

 tained by a magnetizing force too small in it- 

 self to produce any elongation. With hard 

 steel, the critical value of the magnetizing force 

 becomes very high. Nickel continues to retract 

 with magnetizing forces far exceeding those 

 which produce the maximum elongation of iron. 



METEOROLOGY. Dr. W. von Bezold has de- 

 scribed two periods in the history of the sci- 

 ence of meteorology, according to the different 

 methods of investigation that prevailed in 

 them. The first period might be called the 

 elimatological period. It was then that the 

 effort was made, from accumulated observa- 

 tions of the elements affecting the condition 

 of the atmosphere over the globe, to deduce 

 some general rule or principle; and this was 

 sought by calculating the means of observa- 



tions by the month, year, or period. These 

 means were supposed to characterize the cli- 

 mate. Pursuing the lines thus marked out, 

 Humboldt studied the isotherms of the year, 

 of summer and winter, and their distribution 

 over the surface of the globe, and Dove the 

 monthly isotherms and the isanomalies. These 

 means alone could not lead to a knowledge of 

 the mechanism of the atmosphere. It was 

 necessary to consider not general and empirical 

 results, but the variable and continuous course 

 of each of the meteorological factors, and to 

 compare their variations with one another. 

 This was recognized, and a new method of in- 

 vestigation was adopted which may be called 

 the synoptical method. The course which 

 should be followed in this method was indi- 

 cated by Hamberger, of Jena, as early as 1801, 

 who wrote : " Students in different provinces 

 should join hands and observe at the same in- 

 stants the variations of the mercurial column 

 in the barometer and make notes of the con- 

 dition of the thermometer, the appearance of 

 the sky, etc." This is the only means of reach- 

 ing a correct knowledge of the- changing nature 

 of our atmosphere. Buys-Ballot, in 1354, called 

 attention to the importance of daily weather- 

 charts covering a large extent of country. He 

 distinguished between climatology and meteor- 

 ology proper, the former being the study of 

 the manner in which the weather comports 

 itself over a certain extent of country for a 

 considerable length of time ; and meteorology 

 as relating to a particular atmospheric condi- 

 tion, and the inquiry into its origin, the places 

 of its prevalence, and the manner in which it 

 moves over the globe. In 1854 Leverrier, by 

 direction of Napoleon III, organized a tele- 

 graphic weather- service in connection with the 

 observatory in Paris, and published the first 

 series of daily weather-charts. The applica- 

 tion of these methods soon made it clear that 

 atmospheric movements are not the simple re- 

 sults of polar and equatorial currents, but are 

 connected with points of maxima and minima 

 pressures ; that the air escapes in all directions 

 from the former, and plunges likewise in all 

 directions toward the latter, but in neither 

 case following the radii of a circle, for the di- 

 rection of the winds is always oblique to that 

 of\ the center which they are approaching or 

 from which they are removing. This, the law 

 of Buys- Ballot, is the law of all atmospheric 

 movements. The researches of Ferrel in the 

 mathematical mechanics of the atmosphere 

 have complemented it and given it the char- 

 acter of a general law. This law, with the 

 synoptical method of observation, furnishes 

 a ready explanation of the origin of rains. 

 As the charts show that the air is precipitated 

 from every direction toward the minimum, 

 and yet the minimum is not destroyed 

 that is, the depressions are not filled up it 

 must be admitted that there is an ascending 

 current at this point. Above the maximum, 

 on the other hand, there is a descending cur- 



