614 SCIENTIFIC RECORD FOR 1883. 



cuits, the one inducing, containing a constant battery, and the other 

 induced, are placed near each other. Whenever the former circuit is 

 opened or closed, or is shunted, an instantaneous current is produced 

 in the second which is measured by an electro-dynamometer. If the 

 battery be constant and no other variation occurs, the theory is easily 

 confirmed. This distinguishes these methods from the corresponding 

 galvanometric method, the electrodynamic actions depending on the 

 law of variation of the inducing current, while the magnetic action of 

 the induced circuit depends only on the final state of the inductor. 

 The two bobbins may be placed both on the inductor or both on the 

 induced coil, or one on each. Theory shows that the last is the only 

 arrangement which permits the coefficients of self-induction to be elim- 

 inated. The experimental methods of doing this are described. Bril- 

 louin has described two methods based on the fact that in the electro- 

 magnetic system the ratio of a coefficient of induction to a resistance 

 is a time. !To determine absolutely a resistance, therefore, the essential 

 measurements are (1) the measures of length necessary to calculate the 

 absolute value of a mutual coefficient of induction, and (2) the measure 

 of a time. {Nature, xxvn, 354; Am. J. Sci., III, xxv, 309, 321; Phil. 

 Mag., V, XV, 149; XVI, 144; C. E., XCV, 1348; J. Phys., April, II, II, 

 149 ; July 325; December, 566; Wied, Ann., xix, 106.) 



Bidwell has modified the proportions of the Wheatstone bridge so as 

 to insure the constancy of the current used for measuring resistances 

 by its means. This is important in those cases where the resistance 

 measured is a function of the strength of current. (Phil. Mag., V, XV, 

 316, May, 1883.) 



Chevet has devised a modification of the capillary electrometer of 

 Lippmaun, w r hich is easily constructed and which will show a difference 

 of potential of 0.001 to 0.0001 volt. Through lateral orifices two bottles 

 are connected by means of a piece of thermometer tube. One of these 

 bottles contains mercury, the other dilute sulphuric acid with a little 

 mercury at the bottom, the mercury in each having an insulated plat- 

 inum wire leading to it. These wires being connected together, the 

 level of the mercury and water in the bottles is adjusted so that the 

 surface of separation in the tube is near the end which is in the mer- 

 cury. (C. B., xxvn, 669; Am. J. Sci., December, 1883, III, xxvi, 477.) 



Claverie has also described a capillary electrometer with a horizontal 

 tube, and has given a theoretical discussion of the conditions of sensi- 

 bility in it. It has a displacement of fifteen centimeters for an electro- 

 motive force of one volt, and the zero is fixed. (J. Phys., September, 

 1883, II, II, 420.) 



Debrun has devised a capillary relay, in which the capillary tube 

 being horizontal the motion of the mercury to and fro causes a beam 

 to which it is attached to oscillate on its knife-edges, and so to open or 

 close a secondary local circuit. Since the oscillations are very slow, 

 only about forty-eight a minute, it cannot be used in telegraphy, but 



