214 



XIV. ' ' Account of the Construction of a Standard Barometer, 

 and of the Apparatus and Processes employed in the Veri- 

 fication of Barometers at the Kew Observatory." By JOHN 

 WELSH. Communicated by J. P. GASSIOT, Esq., F.R.S., 

 Chairman of the Kew Observatory Committee of the Bri- 

 tish Association. 



(Abstract.) 



After stating the results of experiments, made under the superin- 

 tendence of the Kew Committee, for the construction of a barometer 

 tube of large diameter by the usual method of boiling the mercury 

 in the tube, the author proceeds to describe a method of filling a 

 tube with the aid of an air-pump. In this process, which is fully 

 detailed in the paper, the tube is so constructed, that when the air 

 has been extracted from it, the mercury enters by atmospheric 

 pressure, provision being made for entirely removing the air which 

 the air-pump has failed to extract. By this method a barometer 

 tube of 1*1 inch internal diameter has been satisfactorily prepared at 

 the Kew Observatory. The author then describes the mounting and 

 mode of observing the standard barometer, proceeds to explain the 

 processes adopted in the verification of barometers, and gives a 

 detailed description of the apparatus for determining the errors of 

 barometers at different atmospheric pressures. 



XV. " On the Aurora/' By REUBEN PHILLIPS, Esq. Com- 

 municated by Professor STOKES, Sec. R.S. Received 

 March 7, 1856. 



In this paper the author enters into various speculations as to 

 the formation and motion of auroral arches. Since it has been found 

 by experiment that the maximum length of the voltaic arc with a 

 given battery is nearly the same in atmospheric air and in highly 

 rarefied air, forming a very perfect vacuum, the author conceives 

 that a streamer begins as a disruptive discharge of finite and very 

 moderate length, (the maximum length very nearly of a continuous 

 discharge,) which starts upwards from the auroral arch, which he 



