82 Proceedings of Pioyal Society of Pdinlurgh. [sess. 
and so on. So that in each of the seven tables for the different 
degrees of wet bulb depression were entered the direction of the 
wind, and the limit of visibility on the different occasions, all those 
for each direction of wind being next each other. 
It is unnecessary to give the whole of these observations, but the 
abstract given in Table ISTo. I. may be useful. In the first column 
of the table is given the direction of the wind, and it applies to all 
the other columns in the table. In the next two columns are the 
observations made when the wet bulb depression was 2°. In the 
first of these two columns is entered the number of observations 
in which the direction of the wind was that shown in the first 
column when the wet bulb depression was 2°, and in the second 
is entered the limit of visibility, being the mean of all the obser- 
vations, the number of which is given in the previous column. 
In the next two columns are entered in a similar manner the number 
of observations and the limit of visibility when the wet bulb de- 
pression was 3°, and in the other columns the number of observa- 
tions and the limit of visibility when the depressions were respec- 
tively 4°, 5°, 6°, 7°, and 8° and over. The number of observations 
taken when the wet bulb depression was over 8° was very small ; 
they have therefore been added to the 8° depression, as they do not 
appreciably affect the result. 
If we examine Table Ho. I. we shall find confirmation of some 
points with which we are already acquainted from the observations 
made with the dust counter. It will be noticed that as the dryness 
of the air increases, the limit of visibility also increases. This is the 
case with the winds from all directions except from the N.E. When 
the wet bulb depression was 2° the E. wdnd had a limit of 10 miles, 
and increased to 22 miles when the air was dry enough to give a 
wet bulb depression of 8°. The S. wind increased from 8 to 32 
miles, the S.W. from 7 to 17 miles, the W. from 50 to 172 miles, 
for the same increase in dryness. The failure of the N.E. winds to 
follow the general law may be due to the figures not being correct, 
Owing to the small number of observations obtained when the wind 
was in that direction. It will be seen that there was only one 
observation with 5° of wet bulb depression, and one observation 
when there was 6°, — far too few to give a result that can be relied 
upon. 
