12 



MAWSON & SWAN, 



ELECTROMETERS or ELECTROSCOPES continued. 



Peltier's (Fig. 79), for measuring the tension of electricity by the 

 deflection of a needle, $ TOS. 



Harris' Balance Beam, for estimating in grain weights the 

 attractive power between two oppositely electrified sur- 

 faces, ^4 4 s. 



FIG. 79. FIG. 80. 



Cuthbertson's Compound Discharging Electrometer, 35/- 

 Thomson's Electrometer (Fig, 80), ^6 6s. 



EXPERIMENTAL APPARATUS. 



Aurora Flask, 4/6 



Aurora Borealis Apparatus, consisting of an egg-shaped globe, adapted 



to fit on to the air pump, with brass foot, 25/- and 2. 

 Bells, for showing the attractive and repulsive power of electricity, 



set of three, 5/6 ; of five on stand, i4/- 

 Bells, set of eight, tuned for Electrical Chimes, 2j/- 

 Biot's Apparatus, to show that Electricity is distributed only on the 



surface of conductors and not on the interior, consisting of a 



hollow copper sphere mounted on an insulating stand, and two 



corresponding half spheres, with handles, i 155. 

 Apparatus for the same purpose, consisting of a hollow copper 



sphere, 5 inches diameter, with an aperture at top, the whole' on 



insulating stand, 16/6 



Metallic Roller, with glass handle, and roll of tin foil, on insulating 



stand, for the same purpose as the two preceding, 25/- 

 Proof Plane, or Electrical Carrier, for use with the above apparatus, i/- 

 Faraday's Butterfly Net, with glass handle, 1/6 

 Do. do. on insulating stand, 3/6 



13 and 15, Mosley-street, Neivcastle-on-Tflie. 



