Dr. Ure on Pyroxylic Spirit. 511 



After this great disturbance the irregularities were still very 

 great; the horizontal-force and the vertical-force magneto- 

 meters partook of similar disturbances throughout. With a 

 few trifling exceptions, an increase of force in one was accom- 

 panied with an increase of force in the other, and so also with 

 respect to the decrease of force. 



The declination magnet has certainly, however, one great 

 deflexion, in which the others have no share ; that which oc- 

 curred between S h 54 m 40 s and 3 h 55 m s , where an arc of 

 1° 12' was described in 20 s . Nothing similar, at this time, is 

 shown by either of the other needles. 



In addition to the observations contained in this account, 

 ample and abundant observations were taken to obtain every 

 variation of the vertical force, and also observations of the 

 declination and horizontal-force magnetometer, sufficient to 

 show every great change and nearly all the small ones, until 

 Sept. 26 d l h a.m., when the observations were discontinued. 



At 4 h 40 m an observation of the dip was taken ; giving a 

 result greater than ordinary. 



The day (Sept. 25) was cloudy throughout : about 9 h p.m., 

 a few bright streamers were seen through the clouds, then 

 nothing more till ll h p.m., when an auroral arch, about 24° 

 high, was visible for a short time. 



It is desirable that accounts of corresponding observations 

 of this disturbance should be collected. I invite observers 

 who may have made observations on the same day, to send to 

 me abstracts of their observations, or to communicate them, 

 in the way which they think best, to the public, or to the 

 persons who are interested in magnetical phaenomena. 



Royal Observatory, Greenwich, 1841, Oct. 26. G. B. AlRY. 



LXXVI. Table of the successive StrengtJis of ' Pyroxylic Spirit t 

 corresponding to its successive Specific Gravities, with some 

 Introductory Observations. By Andrew Ure, M.D., F.R.S., 



fyc* 



11TAVING been professionally employed by an eminent 

 ■*--■■ manufacturing chemist, about eighteen months ago, in 

 experimental researches upon the above spirit, the holzgeist of 

 the Germans, 1 found it necessary to construct the following 

 table, in order to ascertain the commercial value of the article 

 at various densities. The principal use of wood-spirit, as 

 extracted by distillation from pyrolignous acid, or from liquid 

 pyrolignite of lime, is for dissolving shell-lac and sandarac into 

 a varnish for stiffening the bodies of hats, and rendering them 



* Communicated by the Chemical Society, having been read June 1, 1841. 



