380 RECORD OF SCIENCE FOR 1886. 



magnet, and a piece of soft iron is placed within the coil, but free from 

 it, Nvhich concentrates the magnetic force between the poles. The coil 

 is suspended by two silver wires, by which it is in connection witli two 

 binding screws on the base of the instrument. This galvanometer is 

 extremely simple in adjustment and is very dead beat 5 it has also the 

 advantage of being affected to an inappreciable extent by neighboring 

 magnets and currents with a current in its own coils; when no current 

 is traversing it, it is of course quite unaffected. (Nature, April, 1880, 

 XXXIII, 574.) 



Lalande has devised forms of voltmeters and ammeters which might 

 be called electrical areometers. They consist of a bundle of soft iron 

 wires placed inside a metal areometer, which is immersed in a glass 

 cylinder full of water, and round which is coiled the wire through which 

 passes the current to be measured. In the apparatus as constructed a 

 displacement of 10 centimeters corresponds to a strength of from 10 to 

 25 amperes at pleasure, or to a difference of potential of 100 volts. (C. 

 R., CI, ; Phil. Mag., February, 1880, V, xxi, 163.) 



Blyth has described a iiew form of current-weigher for the absolute 

 determination of the strength of an electric current. In one of his in- 

 struments a current of 1 ampere produces an attraction equal to a 

 weight of .01:818 gram. (Nature, September, 1886, xxxiv, 508.) 



Pellat has applied the same principle to the construction of an electro- 

 dynamometer, by means of which the absolute value of a current may 

 be determined within one two-thousandth of its value. (C. R., Decem- 

 ber, 1886, cm, 1189.) 



Bidwell has described an improved form of Wheatstone's rheostat, 

 which is of great use where it is important to adjust a resistance to a 

 nicety or to cause a continuous variation. (Nature, May, 1886, xxxiv, 

 70; Phil. Mag., July, 1886, V, xxn, 29.) 



Eoiti has constructed an electro-calorimeter, formed of two Breguet 

 spirals placed the one above the other; one having the silver on the out- 

 side, the other on the inside. Their opposite ends are fixed and receive 

 the current. Their free ends are connected together and with a metallic 

 index, which they tend to turn in the same direction. A comparison 

 with the electric thermometer of Riess showed for the electro-calorime- 

 ter an equal sensitiveness. This instrument was employed in the elec- 

 trical exhibition at Turin in measuring the Gaulard and Gibbs second- 

 ary generator, and with satisfactory results. (II Nuovo Cimento, xviil, 

 1 ; J. Phys., December, 1886, II, v, 576.) 



Ayrton and Perry have communicated a valuable paper to the Lon- 

 don Physical Society on the construction of voltmeters, particularly on 

 the best method of winding. (Phil. Mag., February, 1886, V, xxi, 100.) 



Wassmuth has suggested that when a galvanometer needle is made 

 astatic by an auxiliary magnet placed at a distance from it, there should 

 be placed in the vicinity of the magnet and perpendicular to its direc- 

 tion a plate of iron. The sensibility of the galvanometer is notably 



