282 
Proceedings of Royal Society of Edinburgh. 
SESS. 
The method adopted in the preparation of this paper was, first, 
to construct a number of tables containing the actual observa- 
tions ; and, secondly, to compare the simultaneous readings at the 
three stations. 
Pressure, Table I. — Barometric pressure was highest, 27'784 
inches, at 21 h. on the 6tli, and lowest, 26’617 inches, at 18 h. on 
the 22nd, the wind being calm on both occasions. The range over 
the 23 days was thus IT 67 inch. The maximum occurred in the 
midst of a period of anti-cyclonic weather, which was pretty general 
over north-western Europe, but the dry weather of which was of 
longer continuance at the middle station than over the rest of the 
British Isles. With the exception of a slight shower on the 3rd, 
no rain fell from that day till the early morning of the 10th, and 
moderate to light winds were the rule till the 9tli. The minimum 
occurred during a period of low-pressure general over the British 
Isles. The wind was squally from the east in the morning, but it 
died away later. During the following night there was a very 
heavy rainfall, amounting to nearly an inch in twelve hours, 
which, however, seemed to be confined to the upper half of the 
mountain. 
Table II. — I have, by means of the “ Challenger ” tables, reduced 
each barometer reading to sea-level. A study of the differences 
between the barometers at the three stations shows that they are 
extremely variable. For example, one would expect that when the 
summit barometer read higher than the base barometer, that at 
the middle would read a little less higher, and, similarly, in the case 
of reading lower. The truth is, that more frequently than any- 
thing else the middle barometer read lower or higher than either of 
the other two. It would be necessary to obtain more numerous 
data before attempting to propound a general law, but it may be 
noted that out of the 22 times that the mid barometer read 
higher than that at the base, 14 occurred close together during 
the first four days of the month, and were followed by a period of 
fine weather; while the remaining 8 were scattered over the 
latter part of the month, and were extremely minute in amount. 
Taking all the observations into account, we find that on the 
average, the mid barometer read 0‘010 inch lower than that at 
Fort-William, after all necessary corrections had been made. 
