432 SCIENTIFIC RECORD FOR 1882. 



pheric electricity and solar physics, recalls attention to the important 

 papers by Barlow on earth currents in the London Philosophical Trans- 

 actions for 1849. {Natttre, xxv, 30.) 



A. J. S. Adams, from observations of earth currents from 18CG to 1883, 

 concludes that these are subject to a diurnal period, dependent upon the 

 l^osition of the moon and the sun, similar to the ocean tides. {Nature, 

 xxiii, p. 42-4.) 



One of the best-marked magnetic storms occurred through out the globe 

 on April 16 and April 1 9, 1882. Mr. W. Ellis of the Eoyal Observatory, 

 Greenwich, has compared together the full photographic traces made 

 by the self-recording apparatus at -that place and at Toronto. He finds 

 that the times or moments of the commencement of the disturbance 

 are in one case two minutes earlier at Greenwich, but in the other case 

 one minute later, indicating that such disturbances are simultaneous at 

 widely distant localities. (There is no evidence that the time-scales 

 of the photographic sheets are reliable to within a minute, or can be 

 read ofl' to within less than a minute. The question of simultaneity will 

 be more thoroughly settled if the International Polar Commission suc- 

 ceed in their proposed eflbrt to look sharply after 'the seconds.) {Nature, 

 XXVI, p. 175.) 



Mr. Scuderer has established at Tortosa a simple arrangement of wires 

 stretched between two houses and connected with telephones and gal- 

 vanometers, so that he observes both ground currents and atmospheric 

 electricity, whether due to condensation of aqueous vapor or to light- 

 ning discharge, or the action of the wind or other occult causes. {Nature, 

 xxv, 23.) 



Warren de la Eue and H. W. Miiller have continued their elaborate 

 researches into electric discharges in vacuo, and present some of their 

 conclusions as to the nature of the auroral light as follows: "Our ex- 

 periments on the electric discharge, which have already been i:)ublished 

 in the Philosophical Transactions and the Proceedings of the Eoyal 

 Society, enable us to state with some degree of probability the height 

 of the aurora borealis when its display is of maximum brilliancy, and 

 also the height at which this phenomenon could not occur on account 

 of great tenuity of the atnuosphere. 



"In Part III of our Electric Eesearches {Phil. Trans., Part I, vol. 

 171) we have shown that the least resistance to the discharge in hydro- 

 gen is at a pressure of 0.G42 millimeter, 845 M ; * after this degree of 

 exhaustion has been reached, a further reduction of pressure rapidly 

 increases the resistance. 



"Although we have not experimentally determined the pressure of 

 least resistance for air, we have ascertained that while the discharge oc- 

 curs in hydrogen at atmospheric i;»ressure between disks 0.22 inch dis- 

 tance, they require to be approached 0.13 inch to allow the discharge to 



* [M is about rsVff of a millimeter.] 



