B. TERRESTRIAL PHYSICS AND METEOROLOGY. 95 

 THE FOUCAULT PENDULUM EXPERIMENT. 



The general interest which centres in the interesting ex- 

 periment known as the Foucault pendulum, will cause math- 

 ematicians and physicists to notice the short memoir of Hull- 

 mann, entitled "A Critical Investigation of the Change of 

 the Plane of Vibration of a Pendulum." In this work the au- 

 thor discovers several inaccuracies in all previous computa- 

 tions on this subject, and suggests in their place a new compu- 

 tation. It is generally understood that, at the pole of the 

 earth, the plane of vibration of a free pendulum remaining 

 constant must make an angle with the movable meridian of 

 the place, which angle, in consequence of the rotation of the 

 earth on its axis, continually increases, until it amounts to 

 360 degrees at the end of twenty-four hours ; that is to say, 

 that after the lapse of one day the plane of vibration returns 

 to its original position. At the equator, the plane of vibra- 

 tion remains always parallel to the meridian ; while at all 

 other points of the earth's surflice, it makes an angle with the 

 meridian which depends upon the latitude of the place, and 

 at the end of twenty-four hours has not yet amounted to 360 

 degrees. The author's special object has been to discover 

 when the pendulum will finally return to the original plane. 

 19(7,1873,296. 



A SCIENTIFIC BALLOON ASCENSION. 



A balloon ascension for the purpose of scientific observa- 

 tion was made on the 26th of April last in Paris, in which 

 five gentlemen participated, under the general supervision of 

 Janssen. This is the first ascension made by these gentle- 

 men, and it is to be hoped will be repeated. After consid- 

 erable training and a careful study of the objects before 

 them, and receiving the suggestions of many experienced 

 physicists, as well as the assistance of the French Society for 

 Aerial Navigation, these gentlemen undertook to study the 

 question of aerostatic triangulation, as well as to make numer- 

 ous meteorological and physiological and other observations. 

 Some of the instruments which they carried were quite 

 unique in their way, among them a holosteric barometer, rat- 

 ing down as low as six tenths of an inch of atmospheric press- 

 ure, and very sensitive and exact an instrument that had 



