66 Scientific Intelligence. 



be withdrawn. On passing now the spark from an induction coil 

 through the fulminate by means of the wires through the stopper, 

 it at once explodes and the walls of the tube are seen to be lined 

 with a deposit of soot mixed with a small quantity of mercuric 

 sulphide and sulphur. If the tube be filled with nitrogen or 

 carbon dioxide the deposited carbon is dense, lustrous and co- 

 herent. Other explosives were ineffectual. — J. Chem. Soc, lv, 

 220-223, May, 1889. G. f. b. 



2. light and Electricity. — Professor Righi (Riv. Sci. Ind., 

 July-August) shows that ultra violet radiations reduce to the 

 same potential two conductors, a plate and a piece of grating, 

 applied to each other, the rays being thrown on the grating side. 

 He suggests a convenient way of measuring differences of poten- 

 tial of contact. One notes the deflection of an electrometer con- 

 nected with the plate (the grating being permanently connected 

 with earth) ; then, having connected the electrometer for an 

 instant with earth, makes the radiations act a sufficient time. He 

 used a zinc electric lamp, and the metals examined were placed 

 in some cases in a bell jar, to which some gas or vapor was 

 admitted. From measurement of different plates with the same 

 metallic net (copper, zinc, or platinum), the differences of poten- 

 tial of pairs of metals could be deduced. Prof Righi found the 

 differences sensibly the same in dry and moist air and in carbonic 

 anhydride : but with hydrogen, very different values (from those 

 in air) appeared, where one of the metals examined was platinum, 

 palladium, nickel, or iron (doubtless due to absorption). In 

 ammonia all the metals, examined with zinc net. seemed to have 

 become less oxidizable ; and in coal gas, carbon and platinum 

 behaved like more oxidizable metals. — Nature, Nov. 7, 1889, 

 p. 18. J. T. 



3. Galvanic Polarization. — E. Warburg has made a careful 

 and long continued study of this subject and concludes that 

 previous observers have not sufficiently taken into account oxidi- 

 zation of the metallic electrode in electrolytes containing oxygen. 

 The metallic electrodes are surrounded thereby with a weak solu- 

 tion of salt of their own metals, and the electromotive force 

 changes with the concentration of this solution. — Ann. der 

 Physik und Chemie, No. 11, 1889, pp. 321-344. j. t. 



4. A Simple modification of the method of Telescope and 

 Scale reading. — The well known method consists in reading the 

 reflection of a scale placed at a certain distance from a movable 

 mirror, in this mirror, by means of a telescope. Since the. tele- 

 scope must be focussed on a reflection which is as far behind 

 the mirror as the scale is in front, the range of adjustment is 

 limited. H. E. J. G. DuBois has modified this method by placing 

 a second fixed mirror in front and inclined to the movable mirror. 

 With a telescope one can then read a division of the scale put at 

 twice the usual distance from the movable mirror. With a 

 telescope magnifying 18 times and with an objective of 3*5 cm one 

 can read to two seconds angular measure. — Ann. der Physik and 

 Chemie, No. 11, 1889, p. 494. j. t. 



