PHYSICS. 615 



the author thinks it useful in automatically registering- instruments, 

 such as barometers, thermometers, and galvanometers. (J. Phys., April, 

 1883, II, ii, 169.) 



Ducretet has constructed a universal galvanometer which is capable 

 of measuring from 0.1 to 100 amperes when used as an ammeter, and 

 from 0.1 to 700 volts wheu used as a voltmeter. The needle is immersed 

 in liquid to damp its vibrations and is con' tolled by a steel magnet 

 beneath it. It is placed at one end of a graduated rule on which slides 

 the coil, movable by a rack and pinion. The coil is wound in a groove 

 in a metal ring, and has a resistance of 5,490 ohms. For measuring cur- 

 rent the metal ring itself is used. The instrument is empirically cali- 

 brated. (J. Phys., December, 1883, II, n, 556.) 



Siemens and Halske have brought out a torsion galvanometer for 

 strong currents. It consists of a magnet suspended between two coils, 

 suspended by a torsion spring so arranged that the amount of torsion 

 required to return it to zero after deflection can be read off directly. 

 Two forms are made, the vertical and the horizontal. In the former 

 the needle is suspended by a silk fiber, the reading being taken from 

 above. In the latter the needle is balanced on a knife-edge and carries 

 a pointer at one end, moving over a scale. The amount of torsion neces- 

 sary to return the needle to zero is indicated by a second pointer, which 

 is attached to a handle, and which also moves in front of the scale. 

 These instruments may be used either in the main circuit or in a shunt 

 circuit. (Nature, October, 1883, xxvin, 571.) 



Obach has improved his movable coil tangent galvanometer by mak- 

 ing the coil compound, the ring itself being used for current, and the 

 coil, which is of high resistance, for electromotive force. The coil 

 revolves about a horizontal axis, and can be fixed at any angle. The 

 needle is suspended and can be rendered dead heat. The coils are so 

 balanced that the same deflection is produced by one volt with the high 

 resistance coil which is produced by one ampere with the low one. (Phil. 

 May., August, 1883, V, xvi, 77 ; Nature, July, 1883, xxvin, 257.) 



Gray has examined the influence of temperature, density, and chem- 

 ical composition upon the electric conductivity of glass. He finds that 

 with the varieties of glass having lime as their basis the poorest con- 

 ductors are those which have a composition most nearly approaching a 

 triplicate, either of potassium and calcium or sodium and calcium. He 

 finds also that among various specimens of lead glass the poorest con- 

 ductors have a composition nearest to a trisilicate of potassium and 

 lead. These latter insulate better, as they are more dense. (Proc. Boy. 

 Soc, xxxin, 256 ; J. Phys., February, 1883, II, II, 95.) 



Foussereau has experimented to determine the effect of hardening 

 upon the electric resistance of glass. He concludes 1st, thaf harden- 

 ing diminishes considerably the electric resistance of many kinds of 

 glass; a specimen of lime glass hardened, and then annealed for six 

 hours at 500°, and observed between 35° and 80° showed 2.30 times 



