286 SCIENTIFIC KECOliD ¥011 1884. 



correct kuowledge, since pure chance would otherwise give the same 

 number of verifications and faihires in each of the classes. {D. M. Z., 

 I, p. 397.) 



107. [We are not able to see any radical difference between the exact 

 method here j)roposed by Dr. Koppcn and the actual experience of the 

 Signal Ofilice since 1873, at which time the expressions allowed to be 

 used in prediction and the method of verifying began to be reduced to 

 rules which have remained in force, except a slight steady change to- 

 ward greater severity. We do not understand that by choosing Ham- 

 burg as an example by which to verify predictions for Northwest Ger- 

 many, he means to imi3ly that in a perfect system one should not take 

 a number of other stations in Northwest Germany, going through a sim- 

 ilar process of verifications for each one and take the average of the 

 whole as representing the general percentage of verification for the 

 whole district; this latter is essentially the process used for each of 

 the districts recoguized by the Signal Ofilice. These districts were at- 

 tempted to be so limited geographically that the average chance of ver- 

 ification at any one station (85 per cent.) should be equal to the average 

 uniformity of geographical distribution of any one feature of the weather 

 over that district,which latter was also estimated at about 85 per cent., 

 and although these limits were fixed in 1871 they have not needed ma- 

 terial change. The criterion just mentioned is evidently that which 

 will give us the greatest economy in the use of words to predict the 

 weather for the whole of a large territory like the United States. It 

 was considered incumbent upon the predictor to distinctly predict for 

 twenty-four hours in advance in regard to the weather, wind-direction, 

 temperature, and pressure changes for every portion of the country, and 

 yet but rarely more than twenty minutes of time was available for this 

 prediction owing to the late hour (11 P. m.) when the observations were 

 made and the imperatve necessity of finishing the predictions by 1 a. m. 

 The necessity for theutmosteconomyof time and words thus led to the use 

 of districts and their limitations in accordance with the above principle.] 



Ill,— (a) Aeronautics; (ft) Thermometers and Dew-point; (c) 

 Barometers; (d) Anemometers; (e) Eain-gauges; (/) Miscella- 

 neous APPARATUS ; [g) Methods of reduction. 



108. The Godard captive balloon seems to be a commercial success, 

 as we see that it has lately been set up in connectiou with the Interna- 

 tional Exhibition at Turin, where short ascents are made, as at Paris and 

 London. Father Denza proposes to have meteorological observations 

 taken from the balloon. [Nature^ xxx, p. 181.) 



109. [The Army Signal Office has arranged for a number of ascen- 

 sions for meteorological observations.] 



110. J. W. Clark, in reference to the condensation of liquid films on 

 wet solids, a matter that is of vital impoi tancc in the use of the dew- 

 X)oint apparatus, submits some notes an<l cxperimeDts which will aftbrd 



