216 Intelligence and Miscellaneous Articles. 



must conclude therefore, with Dove, that there is less dry air in 

 summer than in winter in the northern hemisphere. 



(3) The hygrometric capacity of the air, that is the maximum 



vapour which it can contain, is expressed by tt ,. . But accord- 

 ing as we ascend, the temperature and F diminish, while on the 

 other hand H becomes less also. There are two inverse causes 

 of variation ; experiment proves that the capacity decreases but 

 very slowly. In like manner the richness is always a little less on 

 the summit than at the base of the Puy de Dome. 



(4) The last column of the table measures the total capacity 

 during the night when the temperature is lowest. It is in general 

 greater than the richness at 6 a.m. ; but it is sometimes smaller, 

 from which it may be inferred that the air is saturated at any 

 height when its temperature is a minimum. This explains all the 

 condensations of steam which generally take place in the night. 



f 

 In fine, the values of ^ only tell us the relative degree of dry- 

 ness or moisture ; they do not measure the quantity of vapour. 



f 

 On the other hand, the ratio tj^, gives the hygrometric compo- 

 sition of the air ; it shows the changes which take place at day 

 and night, in summer and winter, at various altitudes and in 

 different latitudes. — Journal de Physique, vol. iii. p. 469. 



ON THE DEFORMATION OF THE LUMINOUS WAVE-SURFACE IN 

 THE MAGNETIC FIELD. BY E. VON FLEISCHL. 



The results of this investigation are summed up by the author as 

 follows : — 



1. That the wave-surface in the magnetic field has undoubtedly 

 in general the form described by me of two surfaces of rotation 

 which intersect one another. 



2. That the form of these two surfaces differs to an extremely 

 small extent from the spherical form ; but that notwithstanding 



3. The spherical form of both parts of the double surface which 

 results from Verdet's law of the cosine, and which with this law is 

 implicitly assumed in all previous inquiries, is only a faint approxi- 

 mation to the true form. And 



4. That the form of the wave-surface in the magnetic field is a 

 double surface made up of two ellipsoids of rotation, which are so 

 displaced in the direction of their greatest axes that they nearly 

 coincide with each other. — Wiedemann's Annalen, No. 6, 1885. 



