Royal Society. 305 



or streamers, as they are called, generally make their first appear- 

 ance in the north, and as they rise from the horizon assume the 

 form of an arch, extending from east to west, and having its vertex 

 in the plane of the magnetic meridian ; the arch itself being at right 

 angles to the plane. While the arch is near the horizon, its breadth 

 from north to south is considerable, and the streamers of which it is 

 composed appear to be nearly at right angles to the general line of 

 the arch, their directions converging to a point a few degrees to the 

 south of the zenith. As the arch moves forward towards the south, 

 its lateral dimensions appear to contract, the intensity of its light 

 increases, and the direction of the streamers, still tending to the 

 same point in the heavens, approaches more nearly to parallelism 

 with that of the arch. When it has passed the zenith, and arrived at 

 the above-mentioned point, a little to thesouthof the zenith, the arch 

 is seen as a narrow belt, three or four degrees only in breadth, and 

 with well-defined edges. In its further progress southwards it again 

 enlarges in breadth, and exhibits in a reverse order the same suc- 

 cession of changes as before. Hence the author concludes that the 

 streamers have individually a position nearly vertical or parallel to 

 the magnetic dip ; and they form a thin fringe, stretching often to a 

 great distance from east to west, at right angles to the magnetic me- 

 ridian, and that the movement of the fringe from north to south takes 

 place by the extinction of streamers at its northern side, and the for- 

 mation of new ones contiguous to its southern side. 



From a variety of observations which were detailed in this paper, 

 the author infers, in opposition to the opinion of iVIr. Dalton, that the 

 region occupied by this meteor is above, but contiguous to, that of 

 the clouds, or at least to that in which aqueous vapour is condensed, 

 so as afterwards to appear in the form of clouds. The height of this 

 region he estimates as in general about two thousand feet above the 

 surface ; and he is of opinion, that while such is the height of the 

 lower ends of the vertical streamers, their upper ends may have an 

 elevation of two or three thousand feet more. 



Feb. 5. — A paper was read, intitled, " On a Differential Baro- 

 meter," by the late William Hyde WoUaston, M.D. F.R.S. Com- 

 municated by Mr. Warburton. 



The instrument described in this paper is capable of measuring, 

 with considerable accuracy, extremely small differences of barome- 

 tric pressure. It was originally contrived with the view of determin- 

 ing the force of ascent of heated air in chimneys of different kinds ; 

 but as its construction admits of any assignable degree of sensibility 

 being given to it, it is susceptible of application to many other pur- 

 poses of more extensive utility. A glass tube, of which the internal 

 diameter is at least a quarter of an inch, being bent in the middle into 

 the form of an inverted syphon, with the legs parallel to each other, 

 is cemented at each of its open extremities into the bottom of a sepa- 

 rate cistern, about two inches in diameter. One of these cisterns is 

 closed on all sides, excepting where a small horizontal pipe opens 

 from it laterally at its upper part; while the other cistern remains 

 open. The lower ])ortion of the gla^s tube is filled with water or 

 N. S. Vol. 5. No. 28. April 1829. 2 II other 



