334 SCIENTIFIC RECORD FOR 1884. 



general propositioD, but distinctly as a special hypothesis appropriate 

 to a miiuber of practical examples, and tliat in general such restricted 

 hypothetical cases must first be solved before we can, in the present 

 state of our knowledge, proceed to the general solutions which are now 

 imi)0ssible. {Z. 0. G. M., xix, p. 480.) 



261. Prof. A. Oberbeck, commenting upon the memoir of Marchi, 

 states that his own investigations have led him *o a different conclu- 

 sion. In the first place the expression Wirbelgeschwindigkeit (which 

 is not used by Helmholtz) is not properly applied to the movements 

 represented by Marchi by the letter C ; in the second place the conclu- 

 sion that C cannot be zero for any length of time over a large space is 

 incorrect; in general the formula for the motion of the air as given by 

 Guldberg and Mohn is at present the best for comparison with the 

 observations; and if the latest researches of hydrodynamics are to be 

 considered, this can best be done by the formulae given by Oberbeck in 

 Wiedemann's Annalen for 1882. {Z. 0. G. M., xix, p. 489.) 



262. iMiller-Hauenfels in his Theoretical Meteorology endeavors to de- 

 duce philosophically from fundamental principles of mechanics and 

 physics all the principal phenomena of the atmosphere. He first shows 

 that the density of the atmosphere from the poles towards the equator 

 diminishes more rapidly than has heretofore been supposed. Since the 

 unequal warming of the strata of air disturbs the equilibrium it becomes 

 the office of the winds to.endeavor to restore this normal density. By 

 studying the isosteres, or lines of equal density of the air, he finds sim- 

 plified laws for the wind movement, based on the principle of continuity. 



The trade- winds girdling the earth can send no equatorial currents 

 towiird the pole, but constitute a circulation of their own on both sides 

 of the equator. The author shows considerable dexterity in unraveling 

 the complicated phenomena, and his work is worthy the study of mathe- 

 matical and physical meteorologists. {Z. 0. G. 31., xviii, p. 483.) 



263. Dr. Vettiu, of Berlin, according to Koppen, more than 25years- 

 ago published in volume 102 of Poggendorf's Annalen the results of his 

 experiments on movements in the atmosphere. These experiments, 

 together with his equally long continued observations ui)on the clouds, 

 form an invaluable contribution to our knowledge of aerodynamics, 

 affording, as they do, abundant opportunity for testing mathematical 

 theories. A number of these experiments are described by Vettin in 

 the Journal of the German Meteorological Society, and will, it is hoped, 

 lead to the complete publication of his work, as he seems to be able to 

 reproduce nearly all the phenomena of storms. (J). M. Z., i, p. 227.) 



264. Prof. Osborne Reynolds has communicated to the Eoyal Society 

 of London an experimental investigation into the motion of water, which, 

 from its comprehensiveness, constitutes an important contribution to 

 our knowledge of hydrodynamics; the innumerable ingenious experi- 

 ments, the empirical formulae and curves, and the comparison with de- 

 ductive or theoretical formulce mark an advance in our knowledge that 



