554 SCIENTIFIC RECORD FOR 1883. 



from this irregular refraction combined with the regular atmospheric 

 spectral dispersion. {Z. 0. 0. M., xvn, p. 296.) 



XII. — MISCELLANEOUS APPLICATION. 



Koppen gives an abstract of Hann's paper on barometric hypsome- 

 try that was published in 1876, but seems as yet little known, although 

 the main novelty, i. e.. Hann's formula for decrease of vapor tension with 

 altitude, has been utilized in Upton's and other hypsometric formulae. 

 Koppen indorses heartily Hann's method of approximating when the 

 observations of humidity have not been made at either statiou, namely, 

 to assume a probable value of the relative humidity at the time as being 

 better than Banernfeiud and Schrieber's suggestion to adopt a normal 

 monthly value for the locality, since the absolute humidity varies much 

 more than the relative. By assuming the vapor tension, /(e) as ap- 

 proximately dependent principally upon the air temperature, t, Hann 

 finds from winter and summer observations in the Alps and Himalaya 

 f (e) = 0.00154 + 0.000341 1, and introducing this into his formula obtains 

 as a modified factor for the temperature correction 0.00400, exactly agree- 

 ing with La Place. 



Possibly a still better method is the following : By means of annual 



and monthly means of pressure (B and b) and temperature (f and t") at 



two stations determine the temperature constant; for St. Bernard and 



Geneva from 6 years of observation Hann finds 



B /" t ' 4- t" \ 

 h = 18540 log j( 1 + 0.0032 -^ J 



and similarly for other parts of the world. From this data determine 

 the effect of geographical location on these constants and deduce a gen- 

 eralized formula for application anywhere. (Z. O. O. M., xvn, p. 70.) 



Angot replies to a review of his hypsometric formula and tables by 

 maintaining that the diurnal and annual periodicity in altitudes as com- 

 puted ordinarily is a physical necessity that ought not to be diminished 

 or suppressed by any method of computation, but rather brought out 

 in its rational proportions until the rational physical formula for its cor- 

 rection can be deduced. He seems to consider that since the warming 

 of the atmosphere causes a part of what was below the upper station to 

 rise by expansion until it is above, there is therefore less air between 

 the two stations, and the barometric difference, as well as the computed 

 hypsometric difference, should be less during day and summer than 

 during night and winter. 



Hann replies to this insidious error that the temperature term in the 

 Laplace, Angot, Buhlmann, and other formulae would wholly correct 

 this diurnal and annual periodicity if only the true air temperature 

 were known and used; the trouble is neither in the local peculiarities nor 

 in the barometer nor the formula : the periodicity in barometric hyp- 

 sometry is not a physical necessity nor a fact in nature ; it is a result of 

 computations based on man's ignorance of the air temperature and of 



