242 PHYSICS. 



began to creep away from the glass, scarcely wetting it, and no doubt 

 was entertained that soon the phenomenon seen in Quincke's tubes would 

 appccir, and the acid would roll about in the tube like mercury. The 

 explanation is that these peculiar capillary phenomena are due to a thick 

 layer of gas that is condensed over the surface of the glass. — {Nature, 

 XX, 291, 1880.) 



De la Rue and Miiller, reasoning from their electric researches on the 

 spark in rareiied air, believe themselves entitled to conclude on the 

 probable height of our atmosphere. The least resistance to an electric 

 discharge in hydrogen is obtained at a pressure of 0.642™™, or 845 M 

 ,(M signifying millionths of an atmosphere). When it reaches .002™™, or 

 3 M, the dischargeorily just passes with a potential of 11,000 silver chloride 

 •eells (11,330 volts). At the highest exhaustion, 0.000055™™, or 0.066 M, 

 MO discharge took place with the 11,000 cells, but even a 1-inch spark 

 failed to pass. Since a discharge at atmospheric pressure which occurs 

 in hydrogen at 0.22 inch takes place in air only at 0.13 inch-, the authors 

 . conclude that the least resistance for air is at 0.379™™, or 498.6 M. This 

 pressure would be reached at a height of 37.67 miles above the sea. 

 Hence here the auroral discharge would have its maximum brilliancy, 

 and would be visible- 585 miles. The best vacuum produced, 0.066 M, 

 corresponds to a height of 81.47 miles. At this height the discharge 

 would be considerably less brilliant. At a height of 124,15 miles the 

 .pressure would be only .00000001™™, or 0.00001 M, and at such a heighti 

 it is not conceivable that a discharge would occur with any i>robable' 

 potential. At a pressure of 62™™ the discharge has the we!l-known car- 

 mine tint of the aurora. This corresponds to an altitude of 12.4 miles. 

 .At a pressure of 1.5™™ it becomes saluion-tint, and at 0.8™™ much paler. 

 Above this exhaustion it becomes a pale milky white. — {Nature, xxi, 33, 

 1880.) 



Debrun has suggested an imjiroved barometer, which lie calls am 

 amplifying barometer. It resembles the Fortin instrument in general;, 

 but the i)oint marking the zero is at the top of the tube. The cistern 

 has a secoiul tube in its top, open to the air, and into which the mercury; 

 rises, so that the reading is the difference of the levels of the mercuryj 

 surfaces in the two tubes. A third and narrower tube, also open attop'i 

 passes through the top of the cistern. This cistern is larger than ordi' 

 nary, and contains water above the mercury, into which this tube dips, 

 and which rises into it, the level being read by means of a graduate* 

 scale. Any variation of the height of the mercury is multiplied in th' 

 water-column in the ratio of the section of the cistern to that of th 

 water-tube. Hence the sensibility of such a barometer is equal to tha 

 of the water-barometer. — {J. Phijs., ix, 387, ]S"ovember, 1880.) 



Jordan has constructed and erected in the Kew Observatory a baron 

 eter in which the liquid employed is glycerin colored with aniline-rec 

 As manufactured by Price & Co, the glycerin has a specific gravity ( 

 1.26. Hence the mean heiglit of the column is 27 feet, and a variatio 



