io5 



NA TURE 



\_May 29, 1884 



several nights were of exceptional purity so far as regards 

 the definition of stars observed in the telescope. Messrs. 

 Henry say : — 



" We took advantage of the most favourable moments 

 ,0 observe with our refractor of C38 m. the aspect of the 

 principal planets ; Saturn and his rings attracted our 

 especial attention. The representations of this planet 

 were often of remarkable precision, even when magnified 

 more than a thousand times. It was possible to notice 

 on several occasions curious inequalities in the equatorial 

 band. Outside the known rings we established, around 

 the principal separation (Cassini's division), the existence 



of a new ring, brilliant and perfectly defined, having a 

 breadth of about lh". It is surprising that this ring, 

 which is quite visible, has not hitherto been perceived. 

 But the fact which more particularly struck us in observ- 

 ing Saturn, and which has induced us to publish the 

 accompanying sketch, is that, notwithstanding extremely 

 favourable conditions of visibility, it was impossible to 

 discover the least trace of the external a/isc (Encke's 

 division). That division, indicated since Encke by all 

 the observers who have published drawings of Saturn, 

 and which we believe we had also seen with instruments 

 of moderate power, may well be only the result of an 



optical illusion. This phenomenon would be produced, 

 in our opinion, by the brilliant ring which we have dis- 

 covered, and which irradiation causes to appear larger 

 than it really is, while by an effect of contrast we believed 

 we saw, like a black line of separation, what in reality is 

 only a marked difference in the brightness of the rings. 

 By examining at a distance of about three metres the 

 sketch here given, this division may be very clearly noticed 

 as it is usually represented. The experiment will succed 

 even better if one takes the precaution of slightly closing the 

 eyelids. In these conditions the aspect of the drawing is 



pretty much that which Saturn presents when observed 

 with instruments of ordinary dimensions, or even with 

 powerful telescopes when the definition is imperfect. Wc 

 may then explain by an optical illusion these difference;, 

 of aspect observed in the external ring, without its being 

 necessary to attribute them to any modification which has 

 taken place in this curious appendage of Saturn. This 

 interesting planet is now too near the sun for useful 

 observations to be practicable. We shall continue our 

 researches by means of powerful telescopes at the next 

 opposition." 



EARTH CURRENTS '" 

 ^~\NE of the most interesting subjects dealt with at the 

 ^-^ recent Electrical Congress in Paris was earth cur- 

 rents. The absence of published information in France 

 on the behaviour of these erratic disturbers of telegraphic 

 peace has led In an elaborate and careful study of the 

 whole question by M. Blavier, the well-known and dis- 

 tinguished director of the High School of Telegraphy of 

 the Post and Telegraph Administration in France. This 

 has been printed, published, and circulated by the .Minister 

 of Posts and Telegraphs (M. Cochery) for the use of the 

 members of the recent Congress. 



These earth currents are always present in telegraph 

 lines, varying in geographical and electrical direction and 



1 " Etude des Cgu] ants Telluriques,'' par E. E. Blavier. (Paris: Gauthier- 



in strength, generally scarcely perceptible, but sometimes 

 acquiring such intensity as to acquire the title of "storms.'' 

 Their direction depends upon the direction of theirearth ter- 

 minals, and in no way on the route of the wires or on the fact 

 of their being overground or underground. The longer the 

 line the greater their strength. Their strength and direction 

 \ ary with the hours of the day, and they show well-marked 

 periods of maxima and minima. In fact there appears to 

 be a tide in their affairs clearly following solar influence, 

 and it has been believed by more than one observer that 

 the influence of the moon is also perceptible. There 

 is also an annual period of maximum and minimum, 

 and this follows the well-marked eleven-year period of 

 sunspots. We have just been passing through a period 

 of maximum intensity. 1S81 and 1882 were years of con- 

 siderable activity. Their vagaries are exactly coincident 



