66 J. Bridges Lee — Instrument for determining tlie dew-fall. [March, 



The great tide wave, of which we have full evidence on the tidal dia- 

 grams, was felt, as was to be expected, a considerable time after the shock, 

 varying with the distance and other causes, such as wind and its velocity 

 of translation, which again varies with the depth of the water at any given 

 point. 



The wave reached Port Blair first at 8h. 10m., or, if we assume the 

 foregoing idea of the locality of the centre of disturbance and time of the 

 original shock, in 35 minutes, with an average rate of 62 miles per minute. 

 It reached Madras and Negapatam at lOh. 10m., two hours later than Port 

 Blair. These places are 614 and 640 miles from the assumed centre, and 

 this would give a velocity of 4 miles per minute. 



At Paumben the first wave came in at llh. 35m., or more than one 

 hour later than Negapatam ; but owing to the intervening land and straits, 

 I do not think an}' estimate of velocity can be made. At Vizagapatam 

 the wave arrived at lOh. 48m., about 40 minutes later than Madras, giving 

 a velocity of 2*9 miles per minute. At False Point the wave arrived at 

 llh. 12m., or 24 minutes later than at Vizagapatam, giving the same 

 velocity of 2 9 miles per minute. The wave reached Dublat at 1 p. M., 

 giving a velocity of a little over two miles per minute. 



The direction of the wind all day was N. N. E , which would tend to 

 reduce the velocity of the wave on its road to the northern ports. 



2. A New Meteorological Instrument for determining the quantity of dew 

 deposited on clear nights. — Bg J. Bridges Lee, M. A., F. G. S., 

 F. C. S., F. Z S. (Vide Plate VI). 



There is much to be said upon the importance of securing a regular 

 register of the so-called dew-fall aad upon various meteorological problems 

 connected therewith. When sufficient leisure is available, I propose to 

 offer some detailed observations to the Society upon some of those pro- 

 blems : meanwhile the present non-existence of any satisfactory dew-record- 

 ing apparatus at our Meteorological Stations must strike all persons inter- 

 ested in the study of atmospheric physics as a serious defect, and that 

 defect I would seek to help to remedy by describing an instrument which 

 will afford a fairly accurate register and can be made self-recording. 



Description. 



(1.) Take a long deep hollow cylinder of glass, porcelain or earthen- 

 ware. Protect this externally by wood or metal, and fit it with a frame- 

 work or stand which will support it firmly in a vertical position. 



(2.) Take a quantity of pure mercury sufficient to fill f or f or more 

 of the whole cylinder. Pour this into the cylinder. 



(3.) Take a short solid cylinder of Platinum, the diameter of which 

 ehall not exceed i or i of the internal diameter of the cylinder. 



