PHYSICS. 497 



adjourued to meet ou the first Mouday in October, 1883. {Nature^ 

 I^ovember, December, xxvii, pp. 18, 144.) 



Several excellent exiDositions of the absolute or c. g. s. system of 

 electrical units have appeared since the adoption of these units by 

 the International Congress of Electricians. Of these may be espe- 

 cially mentioned a lecture by Levy, delivered before the Soci^te d'En- 

 couragement {Ann. Chim. Fhys., May, V, xxvi, p. 85), and a paper by 

 Pellat (J. Phys., June, II, r, p. 255), 



Clausius has published a paper on the different systems of measures 

 for electric and magnetic quantities, in which he maintains that Max- 

 well has committed an error in his formula for the static magnetism 

 unit. {Phil. Mag., June, V, xiii, p. 381 ; J. Phys., June, II, i, p. 273.) 



To this paper there have been many replies : Everett {Phil. Mog., 

 V, XIII, pp. 376, 431) ; J. J. Thomson {lb., xiii, p. 427; xiv, p. 225) ; Lar- 

 mor {Ih., xiii, p. 429) ; Lodge {Ih., xiv, p. 357) ; Wead {lb., xin, p. 

 530) ; Sargant {lb., xiv, p. 395) ; and finally von Helmholtz {lb., De- 

 cember, XIV, p. 430). The latter says: "In all this I cannot perceive 

 any mistake of Maxwell's; and his equations, derived from the forii:- 

 ulation of the fundamental phenomena chosen by him, are altogether 

 as consistent with each other and as correct, if understood in the sense 

 of their author, as those of Professor Clausius." 



Yon Helmholtz has devised an electrodynamic balance, in which two 

 coils are suspended, with their axes vertical, from the ends of the beam. 

 Above these coils, which can rotate about their axes, are fastened two 

 larger coils. These are so connected that one of the movable coils is 

 attracted, the other repelled. The movable parts are connected with 

 the fixed parts by bands of Dutch metal 8.3 meters long, 6 to 7 milli- 

 meters wide. The instrument will measure to l-2000th a current bal- 

 anced by one gram. ( Wied. Ann., V, xiv, 52 ; J. Phys., January, II, i, 

 p. 52.) 



Sir William Thomson has contrived two new forms of galvanometer, 

 which he calls graded galvanometers, which have for their object the 

 determination of the value sought without calculation. One of these 

 is for measuring differences of potential in volts, and is called a poten- 

 tial galvanometer. The other measures current strength in amperes, 

 and is called a current galvanometer. The plan of both instruments is 

 essentially the same. Each consists of a coil and a magnetometer. 

 The coil of the former instrument is a ring of circular section, l-i""^ 

 in outside diameter and G*^'" inside; the diameter of its section, there- 

 fore, is 4*=". It is made of German silver wire covered with silk, of 

 No. 32 B. w. G., and contains 2,200 yards wound in 7,000 turns, having 

 a resistance of 6,000 ohms. It is saturated with paraffin and served 

 with silk ribbon. This coil is firmly attached to one end of a horizon- 

 tal wooden platform, its plane being vertical. The magnetometer con- 

 sists of a system of magnets properly supported so as to be free to 

 H. Mis. 26- 32 



