380 



Proceedings of Scientific Societies. 



the periodical meteors of August and November, by Sears C. Walker," 

 vi'hich w^as referred to a committee. 



Prof. Bache brought before the society an instrument for measuring the 

 changes in the vertical components of the force of terrestrial magnetism, 

 which he described as combining the principles of the vertical force in- 

 strument of Prof Lloyd, with that of reflection adopted in the magnetom- 

 eters of Prof Gauss, and which had been made for him by Mr. Saxton. 



Prof Bache stated, that having found difficulties in the use, especially 

 by his assistants, of the vertical force instrument invented by Prof Lloyd, 

 and made for the magnetic observatory at the Girard College, by Robin- 

 son, of London, he had applied, in June last, to Mr. Saxton, to construct 

 the instrument now presented to the notice of the society. The details 

 had been matured by conference with Mr. Saxton. The magnetic bar, 

 placed and supported as in the instrument of Prof Lloyd, carries a mirror 

 upon its axis. The mode of adjusting the position of the centre of gravity 

 of the needle does not differ materially from that adopted in the instru- 

 ment referred to. The needle is raised off the agate planes by the action 

 of a screw, raising a bar which supports two small cups adapted to receive 

 two projecting pins on the arms of the magnet. This magnetometer is 

 observed from a distance, like those of Prof Gauss. Prof Bache ex- 

 plained the mode of adjusting the instrument, and of placing the scale and 

 telescopes. 



Prof Bache called the attention of the society to a diagram represent- 

 ing the changes of magnetic declination, as recorded at the magnetic ob- 

 servatory of Mr. Bond, at Cambridge, and at the Girard College, on the 

 magnetic term day of May, 1840, and showing that the changes attending 

 the aurora are not peculiar to one locality, but that, as observed at differ- 

 ent places, they are parts of a great magnetic disturbance. 



