1870.] Proceedings of the Astatic Society. 269 



Col. Hyde then made the following observations on the effe ct 

 produced by a thunder storm on a self-registering indicator — 



" While testing the qualities of the coal from the Baneegunge 

 field, I wished to ascertain the amount of draught in the chimney 

 in use, and the regularity with which it was maintained. 



" For this purpose an ordinary self-recording indicator was 

 constructed, and fixed as follows. 



" At the floor line of the Mint, a hole was bored into the chimney 

 from the Engine room ; in this hole an iron tube one inch internal 

 diameter and six feet four inches long was carefully set in mortar. 

 The tube projected three inches into the chimney and left sufficient 

 outside for the convenient fixing of the indicator. On the outside 

 end of the tube was fixed a tap § inch bore, and this was connected 

 by means of an air tight junction with one stem of a tube of U 

 form, fixed in a block of wood, so that it might stand upright. 



" The diameter of this U tube was 2 T \ inches, and it was filled 

 about half way up with water. Thus one stem of the U tube is open 

 to the inside of the chimney, while the other is open to the room 

 in which it is fixed. 



" Within the stem that is open to the room is placed a light copper 

 ball float, which sits on the surface of the water, and follows the oscil- 

 lation of the water. A thread is attached to this float, and from it 

 passes over a small wheel to a pencil that is free to travel on the 

 line of the axis of a cylinder driven by a clock, after the manner of 

 an ordinary indicator, ( Vide PL V., diagram No. 3,) so that any 

 motion in the water in the XJ tube will be truly indicated by a line 

 drawn on the paper of the revolving cylinder. 



" On the top of the stem of the U tube that opens to the chimney 

 and in the junction is placed a small screw, so that by closing the tap 

 and opening this screw, both stems of the U tube can be opened to 

 the room, and the water in both stems brought to a level. With 

 the float in this condition the cylinder is turned round, and an 

 equilibrium atmospheric line is traced on the paper. The tap 

 is then opened to the chimney, and the screw closed ; after which 

 any diminution of pressure consequent on the current within the 

 chimney is indicated in amount and duration on the paper. 



" It will be seen that the fall of the float and the diagram No. 1 



