ilETEOROLOGY. 389 



0.0002, but the pressure of the vapor of mercury always remains." {Na- 

 tare, xxv, p. 377.) 



At the meeting of the Physical Society, June 23, 1882, Dr. Braun 

 exhibited a somewhat modified Huyghens barometer, which had both at 

 the upper and the lower meniscus of mercury points for exact measure- 

 ment, and which served to measure both the variations and the amount 

 of air pressure. {Nature, Vol. xxvi, p. 240.) 



J. T. Brown communicates to Nature an historical summary of the 

 various forms of barometer, mercurial and aneroid, including self- regis- 

 tering. The various forms which this instrument has assumed during 

 the past two hundred years form a very instructing study and should 

 receive the attention of tho^e novices who are perpetually inventing 

 and patenting the so-called new devices. American literature on this 

 subject seems to have been only partially examined by Mr. Brown, as 

 we find only very imperfect notices or entire omissions of some well- 

 known names. Of foreign names, we especially miss Ernst, Fuess, and 

 Wild & Brauer, of St. Petersburg, and especially Mendelieff, whose 

 method of isolating all gases that may chance to remain in the vacuum 

 chamber seems to us a capital suggestion. (Nature, xxvi, p. 282.) 



In a further communication on his gravity barometer, Mascart states 

 that he made a rough trial of his instrument in his journey to Norway. 

 He finds that it is easily transportable, and its precision is apparently 

 not less than that obtained with the i^endulum. One has merely to 

 observe the mercury-level and the temperature, and the installation 

 may be done in less than an hour in a hotel room. {Nature, xxvi, p. 616.) 



J. Joly, of Dublin, communicates a description of a barometer record- 

 ing by electricity ; the idea being that as the barometer rises and falls 

 an electric current passing through a fine wire dipped in the mercury 

 will have its potential altered by every change in the height of the 

 barometer. {Nature, xxv, p. 560.) 



Hagen makes to the Physical Society at Berlin a report on experiments 

 for measuring the vapor-tension of mercury at various temperatures. 

 The values given by Eegnault are very unsatisfactory. Hagen's a])- 

 paratus consists of a U-shaped tube, by ha\'ing at the lower part along 

 straight tube united to it by fusion, while above either branch termi- 

 nated in a tube twice bent at a right angle and closed at the lower end. 

 By means of a Hagen air-pump this tube-system was gradually evacu- 

 ated to a pressure of x^owo oir ™™ mercury, and the long straight tube 

 opened under mercury at the lower end. The mercury rose in both 

 branches of the U-tube to barometric height. One of the lateral ends 

 of the apparatus was now kept constant at 0"^, while the other was first 

 cooled to — 42° and then heated to various temperatures. Each time 

 the position of the mercury in the two branches was observed with a 

 cathetometer, and the difference of their heights gave the vapor-teusiou. 

 The values so obtained for the vapor-tension of the mercury were less 

 for all temperatures than those given by Eegnault. Thus, e.g., Herr Ha- 



