July 14, If 



♦ KNOWLEDGE 



105 



^iXtY"^" AN ILLLLSJRATF.D ^Jy^ 



^ MAGAZINE OF>CJENCE ^^ ^ 



FLMN LnfORDED-EXACTLY DESCRI BEPj 



LOXDON: FRIDAY, JULY 14, 1882. 



Contents op No. 37 



July Flowers. By Grant Allen Ill 



Ristori's Lady Macbeth 112 



Butterflies aud Moths. By W. J. 



H.Clark 113 



Fire Hisks from Eleetric Lighting... 113 



A Theory of Foresights [IllH.lrided) 111 



AVeathef Diagram for (he Wee]; ... 11.5 



Corresponilence llfi 



Our Mathematical Cu 



THE COMET SEEN DURING THE 

 ECLIPSE. 



By a. C. Ranyard. 



ri"^HE accompanying sketch gives the position of the 

 J_ comet, as shown on my photographs, with some of 

 the more marked rays of the corona stretching out from 

 the sun's liuib on tlie side towards the comet ; hut no 

 attempt is made to indicate the smaller structure of the 

 corona. The scale of the wood-cut nearly corresponds with 



the largest of the photographs. It will he seen tliat the 

 head of the comet is situated at ahout a solar diameter 

 from the sun's limb, and that the tail is greatly inclined to 

 the line joining the head of the comet with the sun's centre. 

 There is a slight curvature of the comet's tail ; but its 

 general direction is such that if a medial line, which we will 

 call the axis of the tail, were produced, it would not pass 

 through the moon's disc. It is evident that this inclination 

 of the tail cannot be merely due to an edcct of per- 

 spective, the tail of the comet being really radial, and the 

 nucleus situated on this side of the sun's centre, or on the 

 opposite side of the corona — for a straight line can only 



be projected into a straight line or a point ;"and if the 

 sun's centre lay upon the axis of the comet's tail pro- 

 duced, the tail, from whatever position it w^as viewed, 

 would always appear as radial to the sun's limb. A little 

 consideration will thow that the inclination of the tail to 

 the line drawn from the sun's centre to the head of the 

 comet may have been greater than it appears in the photo- 

 graph, but it cannot have been less. 



1 hough the fact that the tail of the comet was greatly 

 inclined to the radius vector struck me on first examining 

 the photographs, the probable significance of the fact has 

 only recently occurred to me. Small jets issuing in various 

 directions from the nuclei of large comets have frequently 

 been observed, but these jets do not extend to any 

 great distance from the nucleus ; and, as far as I am 

 aware, they have not been observed extending beyond 

 the outer envelopes of the head of the comet ; while 

 the chief tail into which the envelopes of the head 

 merge streams away in a direction opposite to the 

 sun. If the comet were moving freely in space (that 

 is, not in a resisting medium), and a repulsive force 

 from the sun was the only force acting upon the 

 matter of the tail, we should expect to find the tail either 

 straight, or curved in the plane of the orbit of the comet, 

 when the velocity with which the matter of the tail is driven 

 away is very great, compared with the orbital velocity of 

 the nucleus, we should expect to find a straight, or very 

 nearly straight, tail stretching away from the sun; but if 

 the velocity of the matter of the tail is not very great, 

 as compared with the orbital velocity of the nucleus, we 

 should expect to find a curved tail, with the part in the 

 immediate neighbourhood of the nucleus directed away from 

 the sun, for the matter of the tail on leaving the head of 

 the comet would have an orbital velocity which would carry 

 it onward equally with the nucleus, if undisturbed by a 

 resisting medium, and the small particles of the tail would 

 only drop behind as the motion of the nucleus and particles 

 of the tail were changed by the central forces acting upon 

 them. But if the comet were moving in a resisting 

 medium, the small particles of the tail would lose their 

 orbital velocity more rapidly than the matter of the 

 nucleus, and the tail would have the appearance of being 

 blown backwards by a wind. 



Having regard to the direction of the curvature of the 

 tail, which is slightly concave towards the south, and to 

 the inclination of the general axis of the tail to a radial 

 line drawn from the sun's centre to the nucleus of the 

 comet, we may, I think, assume that the comet was moving 

 in an upward direction, but whether towards us or away 

 from us, and whether it was nearer or more distant from 

 us than the sun's centre, or whether it was coming up to or 

 had passed perihelion, must, I fear, remain a mystery. 



The comet observed by Sir I. Newton in 1G80, and th. 

 comet of last year which was referred to by Jfr. Proctor 

 as having not improbably had its period sliortencd by tlie 

 resistance of the corona, both, probably, passed within a 

 third of a radius of the sun's surface. From general 

 reasoning one would suppose that under the inliucnco of 

 solar gravity the density of the gaseous atmosphere of the 

 corona would increase rapidly as we descend from the outer 

 limits of the corona towards the photosphere, but our want 

 of knowledge with respect to the tfmper.aturo of the 

 coronal area and the behaviour of dust particles and 

 gaseous matter at such high temperatures prevents our 

 tiuiking any useful assumption with respect to the law of 

 increase of density of the solar atmosphere. It is 

 known that in tlic chromosphere at the base of the 

 corona, liydrogcn, and many of tlie terrestrial elements, 

 give a spectrum of narrow lines similar to the spectrum 



