TRANSACTIONS OF THE SECTIONS. 
29 
it is necessary, 1st, that the depressions be considerable in amount; 
2nd, that the dew-points be accurately known. Now neither of 
these conditions is fulfilled by the few registers which have been 
published, the depressions being small, and the observations made 
with an instrument (Daniell’s hygrometer), the difficulty of observing 
with which is universally admitted. It occurred, however, to the au¬ 
thor, that both difficulties might be overcome in the following sim¬ 
ple manner : let air saturated with moisture, and whose temperature 
is therefore its dew-point, be heated, and let the temperature of the 
heated air be taken, as also that shown by a wet thermometer sub¬ 
jected to the action of a current of it. Then, by the application of 
the formula, let the dew-point belonging to the two latter observa¬ 
tions be calculated, and from a comparison of it with the original 
temperature of the air, when saturated with humidity, he expected to 
be enabled to pronounce with confidence upon the value of his me¬ 
thod. Twenty-four distinct observations were thus made, the tabu¬ 
lated results of which justify the following conclusions: 1st, that 
in the case of seven of them the observed and calculated dew-points 
are almost coincident; 2nd, that the difference in no instance ex¬ 
ceeds, and in but one instance reaches, one degree; 3rd, that the 
mean difference deducible from the whole is but *35, or about one 
third of a degree of Fahrenheit. 
At the close of this paper two tables are given by the aid of which 
the application of the formula is rendered extremely simple and ex¬ 
peditious. 
On a New Anemometer . By the Rev. W. Whewell. 
The author described the construction and purpose of an anemo¬ 
meter which he exhibited. The object of the instrument is to ob¬ 
tain a record of the total amount of the aerial current which passes 
the place of observation in each direction. .The assemblage of such 
records for any given time will exhibit a type of the course of the 
wind for such time; the mean of such records at the same place for 
different years will exhibit the annual type of the winds for that 
place, and the comparison of the types of the winds for many dif¬ 
ferent places will throw light upon the general annual movement of 
the atmosphere. Some of these instruments are now in course of 
construction, with a view to their being tried in different places, and 
it is hoped that some account of their working may be produced at 
the next Meeting of the Association. 
Account of the Measurement of the Aberdeen Standard Scale . 
By Francis Baily. 
[This Paper will be printed in the next volume of Transactions.] 
