311 



of terrestrial magnetism, which he described as combining the 

 principles of the vertical force instrument of Prof. Lloyd, with 

 that of reflection adopted in the magnetometers of Prof. Gauss, 

 and which had been made for him by Mr. Saxton. 



Prof. Bache stated, that having found difficulties in the use, espe- 

 cially by his assistants, of the vertical force instrument invented by 

 Prof. Lloyd, and made for the Magnetic Observatory at the Girard 

 College, by Robinson, 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. Sax- 

 ton. The magnetic bar, placed and supported as in the instrument 

 of Prof. Lloyd, carries a mirror upon its axis. The mode of adjust- 

 ing the position of the centre of gravity of the needle does not differ 

 materially from that adopted in the instrument referred to. The nee- 

 dle 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 explained 

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

 telescopes. 



Mr. Peale remarked, that in the November number of the 

 "London, Edinburgh, and Dublin Philosophical Magazine," 

 there were communications "On the Electricity of a Jet of 

 Steam issuing from a Boiler," and stated that sparks, of the 

 kind mentioned, had been observed in a steam-engine at Wil- 

 mington, North Carolina. 



Mr. Boye read a communication, entitled, "On the Perchlo- 

 rate of the Oxide of Ethule, or Perchloric Ether, by Clark 

 Hare and Martin H. Boye," which was referred to a Com- 

 mittee. 



Professors Rogers and Hare referred to circumstances connected 

 with the discovery, mode of preparing, and preserving this highly 

 explosive compound; of which a specimen, dissolved in alcohol, was 

 presented by M. Boye to the Society. Dr. Hare, amongst other 

 matters, remarked, that this is the only ether which is explosive, 

 per se, when transferred from one vessel to another. 



Prof. Bache called the attention of the Society to a diagram 



