302 SCIENTIFIC RECORD FOR 1884. 



average dew-point, we must add the maximum and minimum values for 

 use in a method siniihir to that which he has pointed out.] 



157. F. Erk, from a study of thirty-three years' self-registered tem- 

 peratures at Munich and a discussion of the theories of Weilenmauu 

 and his predecessors, finds that the best combination of three daily 

 observations of temperature is ^ (7 A. M. + 2 p. m. + 2 x 9 P. M.), and 

 that almost the same accuracy is attained by the following combination : 

 J (8 A. M. + 2 P. M. + 2 X 10 p. M.).' If three observations must be com 

 bined into a sim])le arithmetical mean, then the best combinations are 

 as follows : ^ (6 A. M. + 2 P. M. -f 10 P. M.) and ^ (7 a. m. + 2 p, m. + 

 10 p. M.). l!fumerous other combinations are examined by Erk and 

 their advantages discussed. {Z. 0. G. M., xix, p. 254.) 



158. Prof. K. Weihrauch states that the principal objection to the 

 use of the four components of the wind — north, south, east, and west — 

 as measured in some anemometers, in place of the total velocity and 

 the direction, is said to be, that by it the mean velocity and direction 

 and the velocity of individual directions as well as the mean value of 

 wind force, irrespective of direction, cannot be given. He then proves 

 that this objection is a mistake, at least so far as regards the arithmet- 

 ical mean velocity, which can be found from the sum of the four com- 

 ponents by simply multiplying it by the factor ^. The denominator 4 



is, however, rather small, and the figure 5 will apparently do better. 

 (7). M. Z., I, p. 291.) 



159. Jamin, of Paris, proposes that meteorologists, instead of the rela- 

 tive humidity, shall introduce the quotient found by dividing the weight 

 of the moisture by the weight of the dry air actually found in the same 



volume ; that is to say, for ~ substitute = (^. 0. G. M., xix., p. 408.) 



hj u— e 



160. [This proposition seems not yet to have found very hearty accord- 

 ance. Ai)parently Jamin desires by this substitution to obtain figures 

 that will express both the quantity of moisture in the air and its relation 

 to the quantity required for saturation. As he expresses it, the new ratio 

 gives us the hygrometric constitution of the air, and shows the changes 

 that are brought about by diurnal and annual variations at different 

 altitudes and latitudes. It would seem that if the absolute quantity of 

 moisture in the air is really desired it would be simpler to publish it 

 directly in the shape of the weight or tension of the aqueous vapor 

 alongside of the ordinary percentage of relative humidity, as is in fact 

 frequently done. Simi^lest.of all in our estimation is it to publish the 

 temperature of the air and the temperature of the dew-point, leaving it 

 to the climatologist to deduce such phenomena as most aflect vegeta- 

 tion and animal life, and to the physical meteorologist to deduce such 

 additional data as he may desire. The daily prediction of the dew-i)oiut 

 IS as practicable and desirable as that of temperature ; it is to be hoped 

 that the direct determination of the dew-poipt naay soon be made praC' 

 J/icable for all observers.] 



