446 Mr. W. J. M. Rankine on simultaneous Observations of 



referred to were made, were situated on the north-western face 

 of the Pentland range near its south-western extremity, amongst 

 the sources of the river Almond. Both the gauges were placed 

 as near as possible to the surface of the ground, in open and 

 regularly-sloping pasture, far from any sheltering objects. 



The lower gauge, designated by H, was about 700 feet above 

 the level of the sea, three miles and a quarter to the north-west 

 of the line of summits of the Pentland Hills, about four miles to 

 the north-cast of the range of low hills before mentioned, and 

 ten miles southward from the Frith of Forth. 



The higher gauge, designated by G, was about 900 feet above 

 the level of the sea, or 200 feet above the gauge H, one mile and 

 a half to the north-west of the line of summits of the Pentland 

 Hills, one mile and three-quarters to the north-east of the range 

 of low hills, and two miles and a half from the gauge H in a 

 direction south-by-west. 



8. The rain-fall was recorded by a different observer for each 

 gauge every morning about nine o'clock. Although minute 

 fractions were not attended to in the readings, so that compari- 

 sons between the quantities of rain at the respective gauges on 

 single days are of little value, yet I am satisfied of the accuracy of 

 the result of any comparison embracing a period of several days. 



The vicinity of situation and similarity of aspect of those two 

 gauges naturally caused them to receive the rain-fall of the same 

 masses of cloud, so that very few instances occurred of rain fall- 

 ing at one gauge without a fall also taking place at the other 

 within the space of a few hours, if not simultaneously. 



9. In the first of the annexed tables, therefore, the depths of 

 rain-fall at the gauges G and H are compared for each period of 

 rainy weather. There are seventeen of these periods in the table, 

 varying in length from two to eleven days, and separated by 

 periods of drought. The first period, however, from the I3th 

 to the 20th of July, must be taken with the qualification, that 

 the quantities of rain set down for it are merely the sums of a 

 number of brief showers occurring at intervals. At the foot 

 of the table the total depths of rain are compared for the whole 

 period of observation, 151 days. 



The mean ratio set down at the foot of Table I. in the fourth 

 column, shows that the total rain-fall at the gauge G exceeded 

 that at the gauge H in the ratio of one to one and a quarter. 



The ratios for the seventeen periods of rain deviate from this 

 mean amount, upwards and downwards, in a somewhat irregular 

 manner, but evince, on the whole, a tendency to increase with 

 the approach of winter. 



10. In the second table, the depths of rain-fall at the gauges 

 H and G are compared for each of the calendar months, August, 



