British Association for the Advancement of Science, 315 



ther of the corrections, of which mention has been already made, re- 

 quired to be applied. 



The most obvious method of testing the formula, or that which 

 consists in comparing its results with the dew-points experimentally 

 determined, was last noticed. That such criterion may be decisive, 

 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 (Darnell'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.] 



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