1870.] Proceedings of the Asiatic Society. 271 



the height of the chimney, requisite to a calculation of the amount 

 of the disturbance upon this basis ; but he admitted that he did 

 not think the amount which would result from such a calculation 

 would be nearly so large as that in the diagram. The explanation 

 was, therefore, no doubt insufficient. 



Col. Hyde said — " Some time since, I observed the water in the 

 open stem of the Utube oscillating, thinking that this might, perhaps, 

 be due to the concussion of the atmosphere in the room, where two 

 powerful air pumps, driven by a 30 H. P. Engine were delivering air, 

 I made a careful experiment, by closing the open mouth of the U 

 tube, so as to leave only a very small hole open to the room. There 

 was not the slightest alteration in the oscillations, and it was evident 

 that these oscillations were unaffected by the air pumps, and were 

 solely caused by the action of the chimney draught. It would 

 seem also that the length 6 '-4" of tube \" diameter, and the contrac- 

 tion caused by the -f tap would effectually negative the supposition 

 of any sudden motion (such as is indicated in the diagram) being 

 given to the water in the U tube by concussive action on the open 

 stem, and the diagram I think clearly indicates a diminution of 

 pressure within the chimney in relation to the pressure in the room 

 at the base. 



" The most probable cause seems to be a sudden local diminution 

 in the temperature of the storm space or cloud passing over the 

 top of the chimney. The duration of the disturbance within the 

 chimney is about three minutes as shewn by the time lines, and the 

 extent of the disturbance amounts to f of an inch in diminution of 

 pressure. 



tl The diagram indicates an occurrence that caused a sudden in- 

 crease in the velocity of the current up the chimney, a recurrence, 

 and then a return to nearly the original condition, and its shape, I 

 think, shews an exhausting action through a contracted orifice. 



" I have not any record of the temperature or of the reading of 

 the barometer at the time of the storm ; but the height of baro- 

 meter and the temperature of the air and of the inside of the 

 chimney were recorded at 1.38 and at 2.38 p. m. as follows : — 



1.38 p. m. Barometer, 29.74, air temp. 86, chimney temp. 220. 



2.38 p. m. „ 29.02, „ 84, ,, 245." 



