August 8, 1890.] 



SCIENCE, 



>i 



at the equator (85 metres per second) ; while everywhere beyond 

 latitude 35° there is a west wind which acquires its greatest 

 velocity (379 metres per second) at the pole. In this computation 

 a frictionle^s motion is considered. The distribution of the air- 

 pressure corresponding to this has been worked out by Liebenow, 

 and published in the Natiirwissenschaftlichen Rundschau, Jahr- 

 gang III. p. 387, but it has no practical significance for meteo- 

 rologists. 



Ferrel's reasoning gires for v, the relative linear velocity of 

 rotation, in the latitude ip, the following expression : — 



v^ R a \ COS c4 f ; 



i3eos<i> ' ) 



that is, v = for cos'' ^ ^ | or (^ = 35° 16'. 



For 0> 35° 16', v is positive (west wind). 



For 0< 35" 16', v is negative (east wind). 



Ferrel's and Siemens's researches were independent of each 

 other, but their apparently complete agreement is in reality only 

 a partial one. They agree as to the dividing-line between the 

 easterly and westerly air-currents (the first three being from the 

 east, and the last four from the west) ; but the following little 

 table shows bow widely their computed velocities (expressed in 

 metres per second) differ. 



In both cases there are assumed three facts : (1) The friction is 

 not considered ; (2) The initial condition is relative rest ; (3) 

 Thorough mixing of the air is accomplished by meridional mo- 

 tions. There are certain inaccuracies of deduction existing in 

 both theories, so that we cannot say without qualification that 

 one is right and the other wrong. Siemens seems to have fallen 

 into the error of the Hadley-Dove view, that masses of air passing 

 from one parallel to another retain unchanged their absolute 

 velocity of rotation. It is one of the main points of Ferrel's 

 theory, that this does not remain constant, but increases with 

 the approach towards the axis of the earth. The following quo- 

 tation from Helmholtz's memoir "Ueber Atmospharische Be- 

 wegungen" {Meteorologische Zeitsehrift, 1888, p. 329) shows his 

 complete agreement with Ferrel. He says, " If we consider a 

 rotating belt of air, whose axis coincides with the axis of the 

 earth, and which is pushed first a little to the north and then a 

 little to the south by the pressure of the adjoining similar belt, 

 then, it the friction is not considered, according to the well- 

 known general mechanical principle, the moment of rotation 

 must remain constant." This can be true only when the angular 

 velocity of the belt changes in an inverse proportion to the square 

 of its radius. The two velocities at the poles obtained by Ferrel 

 and Siemens, and given in the table, are both far removed from 

 the true value ; but in either case there would be a crowding- 

 back of the air from the axis of rotation, because such great 

 velocities of rotation are impossible. Ferrel, however, in his 

 further development, so limits the theoretical conditions that 

 these impossible velocities are modified into possible conditions. 

 It is quite amusing that some readers of Ferrel's writings have 

 understood him to make the ridiculous statement that all of the 

 results found by his purely theoretical deductions do actually 

 exist in nature ; and they claim that such absurdities are suffi- 

 cient to cause his theory to be rejected. It merely shows that 

 such persons have only glanced at B'errel's writings. 



(a) The resistances to motion, such as friction and the like, 

 make it impossible that such a great increase as Ferrel and 

 Siemens figure out can occur in the relative motions of the air; 



and Helmholtz has given his views of this action, in the paper 

 previously mentioned. 



(5) Again: the mixing- up of the air does not occur in the as- 

 sumed uniform manner which requires that all the air, no matter 

 what its altitude is, which proceeds from about the latitude of 

 35°, reaches all other latitudes. As an actual fact, we find that 

 the motion toward the pole, towards gradually narrowing circles 

 of latitude, takes place mostly in the higher layers of the atmos- 

 phere, and the opposite motion in the lower layers. According, 

 then, to the law of the conservation of areas, we owe to the upper 

 movements the west wind, and to the lower the east wind. 



The modifications of this simple scheme which are necessary to 

 account for the observed wind phenomena are next discussed by 

 Dr. Sprung, who gives special attention to the recently expressed 

 views of Dr. Peruter (see Wetter, p. 11, 1890; also given in a lec- 

 ture at Vienna, Nov. 7, 1889), concerning the lack of an upper 

 south-west trade-wind between the two pai'allels of 35° latitude; 

 his view being based on the theories of Siemens and Oberbeck, 

 and in opposition to that of Ferrel. Professor Abbe's recent 

 studies of cloud-motions in the tropics will be very useful in this 

 connection. The tendency towards the origination of a tropical 

 east wind is far more marked in the theory of Ferrel than in that 

 of Siemens. That the actual wind circulation as marked out by 

 these two investigators are so contradictory seems to be due to the 

 fact that Siemens simply combined with the weak meridional 

 surface currents the results obtained in (9), without considering that 

 this is sensibly changed by the conditions explained under (6). 

 Ferrel, on the contrary, carefully investigated the gradients of air 

 pressure, and found that the east wind of the tropics could be 

 perceived to only a limited extent. 



Sprung's trite references to the recent works of Oberbeck (Sitz- 

 ungsberichte Berlin Akademie, March 5 and Nov. 8, 1888) and 

 Moller (Archiv der Seewarte, vol. 10), and his own attempt to 

 treat this question of the upper anti-trades in an empirical manner, 

 cannot be discussed in the present short communication. The 

 last section (five pages) of Sprung's paper is of special importance 

 to the student of this question of general motions, for he treats 

 analytically the reasons for the use of the principles adopted in 

 Siemens's paper. Frank Waldo. 



Mount Lake Park, Md., July 29. 



A Brilliant Meteor. 



On Sunday night, July 27, at 11.15 p.m., whil^ sitting on the 

 piazza looking west, I saw a remarkable meteor, which in size 

 and slowness of movement resembled that of 1861 (which I also 

 saw). 



It appeared from beneath the edge of one of the fleecy streaks 

 of cloud with which the sky was full, about forty degrees 

 above the horizon. Its path was downward, very slightly south- 

 ward. When it first appeared, it rapidly increased in size to a 

 large sphere of brilliant white light, changing immediately to a 

 pale apple- green as it descended, followed by a train of dark-red 

 glowing particles. Its duration above the horizon was about two 

 seconds. 



The clouds were not thick enough to obscure the light of third- 

 magnitude stars. F. 



Sea Girt, N.J., July 30. 



BOOK-REVIEWS. 



Hypnotism. By Albert Moll (of Berlin). (Contemporary Sci- 

 ence Series.) New York, Scribner & Welford. 8°. 



Having noticed the general plan and scope of this work upon 

 the appearance of the original German edition (Scienc^ July 19, 

 1889), it may suffice to express briefly our appreciation of the 

 value of this contribution to the English literature on hypnotism. 

 We have had a translation of Bernheim's important work, and of 

 KraflEt-Ebbings treatise on the subject from the more strictly 

 medical point of view, and translations of Binet and Fere, and of 

 BjornstrOm, giving more general expositions of hypnotic phe- 

 nomena. It is with the latter class of works that Dr. Moll's invites 

 comparison. It is much fuller and more thorough than Bjorn- 



