1903.] Dust- Figures. Determinations of Magnetic Elements. 211 



" On the Formation of Definite Figures by the Deposition of 

 Dust," By J. AITKEN, F.R.S. Received July 13, 1903. 



(Abstract.) 



The author discusses the experiments in Dr. W. J. Russell's paper,* 

 finding from optical examination of te phenomena that the dust 

 falls out from the layer of air creeping along the lower side of the 

 plate, and this dust-free layer of air turns round the edges of the plate 

 and flows over and in contact with its upper surface, so protecting it 

 from any deposit of dust where the current has sufficient horizontal 

 motion ; but deposition takes place where the motion is checked by the 

 currents meeting, or where obstructions cause eddies and break the 

 stream-lines, or by anything that tends to prevent the dustless layer of 

 air flowing over the upper surface of the plate. 



" Mean Results of Monthly Determinations of the Magnetic 

 Elements at the Valencia Observatory, Cahirciveen., lat. 

 51 56' K, long. 10 15' W." By J. E. CULLUM. Received 

 June 5, 1903. 



Absolute Declination, 1902. 



* ' Roy. Soc. Proc.,' vol. 71, p. 285. 



VOL. LXXII. 



