290 Sir David Brewster on the Polarisation 



into two separate diverging streams, the size of the enclosed 

 angle varying with the intensity of the sound*. Just as with 

 the flame, an increase in the velocity of the current diminished 

 the length of the unbroken stream of air ; and at a great velocity 

 the head did not split, but was brought down close to the nipple, 

 after the manner of the experiments of Dr. Young, to which re- 

 ference has been made. 



Having thus, I think, proved that the main agent which pro- 

 duces the change in a sensitive flame is the vibration imparted 

 to the gas-pipes, it must not be forgotten that the character of 

 the orifice in the burner is a very essential part of the pheno- 

 menon, not only determining the shape into which the shrinking 

 flame is thrown, but also influencing the pitch of the note which 

 most powerfully affects the flame. A small orifice yields a flame 

 affected by higher notes than the flame from a larger orifice, where 

 the velocity of the issuing gas is less, — another expression of a 

 fact already stated. There are other phenomena connected with 

 this part of the subject, which may be worthy of future consi- 

 deration. 



XL. Additional Observations on the Polarization of the Atmo- 

 sphere, made at St. Andrews in 1841, 1842, 1843, 1844, and 

 1845. By Sir David Brewster, K.H., D.C.L., F.R.S., $c.f 



SINCE the publication of my " Observations on the Polari- 

 zation of the Atmosphere," J a long and elaborate memoir 

 on the same subject, by Dr. R. Rubenson, has appeared in the 

 Acts of the Royal Society of Sciences of Upsal§. The observa- 

 tions which it contains were made with the finest instruments, 

 and with a degree of accuracy which had not been attempted by 

 previous observers. They were begun at Upsal in 1859, and 

 carried on at Rome between the 6th of June and the 5th of 

 August, 1861, at Segni in the Campagna between the 6th and 

 the 27th of August, 1861, and at Rome from the 5th of October, 

 1861, to the 27th of July, 1862. 



Although Dr. Rubenson has devoted a section of his work to 

 ascertain the cause of atmospherical polarization, another section 



* This observation at once brought to my recollection the result of an 

 experiment I had made, at the request of Dr. Tyndall* some time ago when 

 at the Royal Institution : it was a precisely similar splitting up of a column 

 of smoke under the influence of the energetic vibrations of a large tuning- 

 fork. Whatever merit, therefore, may attach to the priority of this observa- 

 tion does not belong to myself. 



f From the Transactions of the Royal Society of Edinburgh, vol. xxiv. 

 Communicated by the Author. 



t [See Phil. Mag. vol. xxx. p. 118, &c, 1865.} 



§ Ser. hi. vol. v. This memoir has been published as a separate work 

 in 4to, pp. 238. Upsal, 1864. 



