6o6 



NATURE 



{Oct. 3, 1878 



Class I. 

 Ignited Columns. 



a. The apparatus described by 



Prof. Barratt, Phil. Mag. , 

 April, 1867. 



b. Described in this paper, 



Fig. 2, et seq.^ 



Class II. 



Partially-ignited Columns. 



. Described in Nature, vol. 

 V. p. 30. 



. Described in a former com- 

 munication, December 7, 

 1876. 



. Described in ' this paper, 

 Fig. 4, et seq. 



I. a consists of a glass tube with a tapering jet. A V-shaped 

 cut made across the end of the jet renders it more sensitive. If 

 such a jet be connected to a water-supply it will be found to be 

 segmental. If it has the V-shaped groove this will be more 



marked. The primary expansion lies in 

 the groove in most cases. The only use 

 of the latter is to render the column more 

 certainly segmental 



The column being segmental, consists 

 (Experiment II., note) of two streams, one 

 on each side the groove meeting at a very 

 acute angle. 



When there is no groove little irregu- 

 larities in the orifice determine the seg- 

 mentation of the column. The friction of 

 the long, narrow jet and the ignition of the 

 gas at the orifice retard the outflow, and to 

 obtain a sufficient velocity the gas must 

 issue under a considerable pressure * (one 

 or two feet). 



When excited it shortens and expands'at 

 right angles to its primary expansion. 



I. b has been described (Fig. 2, etseq.). 

 The jets meeting at a considerable angle, 

 the column is flattened. It responds in 

 the same manner as the preceding, but the 

 primary expansion being very short, the 

 responding expansion is usually the longer 

 one. 



II. a consists of a tapering jet placed a 

 small distance below a piece of fine wire 

 gauze. The gas is ignited above the gauze. 

 It is very sensitive, but the intersection of 

 the column by the gauze prevents the flame 

 from taking any well-marked form when 

 responding. 



II. b is practically the same as the fore- 

 going. The column being surrounded for 

 a part of its length by the closed tube, 

 remains unignited in this part. 



The excited flame divides distinctly into 

 two parts, which are in a plane at nght 

 angles to the primary expansion. 



This division appears to arise firom the 

 tendency of the excited flame to form a flat 

 expansion, and the edges being reflected 

 from the inside of the tube, because the 

 same jet when used without the tube and 

 under a high pressure, does not divide, but 

 produces a fan-shaped expansion. 



II. c is shown in Fig. 4. The flame from B keeps the column 

 beyond it heated to the ignition point. It is of interest as 

 showing the use of the gauze in II. a and the tube in II. c, and 

 further, that the value of the tube in the latter does not depend 

 upon its resonance. 



In Experiment IV. it is shown that a sensitive-flame, when 

 emitting a note, sends out an expansion at right angles to the 

 primary one, the same behaviour being observed when the flame 

 is excited by an external sound. It therefore follows that if 

 these actions are conversely related to each other, that a 

 responding flame should emit a note. This will always be 

 found to be the case ; but the sound being usually very feeble, 

 may escape observation unless some means be adopted to con- 

 centrate it [vide Experiment VII.). 



The expansion occurs just above the intersection of the axes 

 of the jets. Call these a and b. The two columns strive for a 

 mastery of direction, a overcomes b and sends a tongue of flame 

 through the primary expansion, but the partial stoppage of b 



Lecomte has previously shown that the fish-tail burner is sensitive. 

 .*^y making a V-groove across the end of a partially-closed tube, this 

 kind of jet becomes tolerably sensitive at a pressure of three inches 



Fi^. 5. 



causes an increase of pressure by which in turn it overcomes a, 

 and sends a tongue of flame through the other side of the primary 

 expansion, and so on. These movements succeeding each other 

 with very great rapidity in a high note, and gas being highly 

 elastic it is impossible to recognise them separately. Experi- 

 ment XIII. shows how the impulses may be obtained so slowly 

 as to be individually perceived. 



When the gas pressure is so low that the column is quiescent, 

 a sound is necessary to start the operation ; and further the 

 sound must so strike the component columns as to give one of 

 them an advantage {vide Experiment VI.). 



I have only referred to water columns as far as was necessary 

 to illustrate the behaviour of gaseous ones. They should form a 

 subject for separate consideration. 



Summary. 



1. A fluid column if sensitive to sound consists of two columns 

 meeting at an angle (Experiment II. note). 



2. The resultant of the two columns is an expansion (Experi- 

 ments II. and III.). 



3. A column so constituted will under favourable conditions 

 emit a note (Experiment IV.). 



4. If excited by an external sound, it takes the same form as 

 when it spontaneously emits the sound (Experiment V.). 



5. A column excited as in 3 and 4 sends out an expansion at 

 an angle (usually a right angle) to the primary expansion. 



6. The component column of a sensitive column must be at 

 such unequal distances from the sounding body that they are not 

 thrown into the same phase of vibration (Experiment VI. and 

 note). 



7. A gaseous column increases in sensitiveness with the pres- 

 sure, i.e., the velocity. 



8. A gaseous column is lessened in velocity by ignition at its 

 origin (Experiment VIII.). Hence — 



9. A gaseous column when ignited is less sensitive than when 

 unignited (Experiment IV.). R. H. RiDOUT 



THE AURORA OBSERVATIONS OF THE 

 AUSTRO-HUNGARIAN ARCTIC EXPEDI- 

 TION, 1872-74, BY CARL WEYPRECHT 



"T^HE Austro-Hungarian Arctic Expedition of 1872-74 was in 

 ■*• many respects an unfortunate one. Not only was the first 

 winter occupied with an unintermitted struggle with the ice, 

 which from hour to hour threatened to crush the ship, and ren- 

 dered it imperative that everything should be in constant readi- 

 ness for her sudden abandonment, but in the second year this 

 had actually to take place, and, on account of their bulk, valu- 

 able records of scientific observation were unavoidably left 

 behind, and among these was the carefully-kept journal of 

 northern-light observations. 



Under such discouraging conditions the mass of valuable 

 observations which Lieut. Weyprecht has succeeded in collecting 

 from the meteorological and magnetic journals and other sources, 

 are interesting not only on account of their many positive contri- 

 butions to our knowledge, but as an example of wonderful 

 scientific industry and devotion. 



Spite of the perpetual changes of the aurora, Weyprecht con- 

 siders that its appearances may be classified under five distinct 

 forms, viz., the arch, the ribbon or streamer, the rays, crown, 

 and haze (Bogen, Band, Fdden, Krone, and Dunst). His de- 

 scription of these forms differs in several particulars from those 

 common in lower latitudes, so that we may be excused for 

 noticing them at some small length. 



Arches {Bogen, arcs) are of regular form ; the highest point 

 closely coincides with the magnetic meridian and the ends cut 

 the horizon at points equi-distant from it. They usually move 

 either northward or southward, rising from the edge of a • low 

 dark segment near the horizon, or again vanishing into it. 

 The rim of light which edges this dark segment is probably 

 only a low and distant bow, or possibly the combined effect of 

 all the remoter arches which are melted into each other by 

 distance and perspective. This is the more likely since a bow 

 is never observed to sink wholly below the horizon, but fades 

 into this distant rim, and, conversely, from it, arches frequently 

 arise and separate themselves as they get higher. Not unfre- 

 quently the arches sink back to the point from whence they 

 arose ; at other times they gradually fade away as they near the 

 zenith, or after they have passed it. Very intense displays never 

 take the form of regular arches. 



