Februaky 1, 1894.] 



KNOWLEDGE. 



35 



The comet was observed here with the twelve-ineh 

 refractor, on the morning following its announcement. 

 Nothing seen during the measures of its position suggested 

 that any phenomena of an extraordinary character would 

 be recorded on the photographic plate ; but the comet 

 could only be examined for a few minutes before dawn 

 would stop an exposure. It was, however, decided to try 

 a plate the next morning, to see what might result from a 

 short exposure. The time of dawn did not permit of more 

 than half-an-hour, but the photograph was satisfactory 

 and interesting, though it showed nothing of special 

 interest about the comet, except that the tail was longer 

 than had been expected from the eye view of it obtained 

 with the twelve-inch refractor. The photogra-phic plate 

 also showed two small short "whisker" tails springing 

 from the head of the comet, on each side the main tail 

 (which itself was split along its axis into two strands). 

 The mornmg of the 20th proved cloudy, but on the 21st 

 another exposure was made to see if any change was 

 taking place. No special change was noted, however, 

 except that all the features were more strongly marked. 

 The main tail, as before, was essentially straight. 



The next morning the twelve-inch showed that some 

 disturbance had taken place, for the tail near the head 

 was distorted. An exposure was at once begun with the 

 Willard lens. The resulting photograph was indeed 

 remarkable (see the picture for October 21st). The tail 

 now presented the aspect of a torch streaming in the wind. 

 The appearance was precisely what we should expect had 

 the comet's tail, in its flight through space, swept across or 

 through some medium dense enough to break up the tail. 

 I cannot see how anyone comparing this with the picture 

 of the 20th, can escape the conclusion that the tail did 

 actually enter a disturbing medium which shattered it. 

 This theory is, I think, further upheld by the third of these 

 pictures, taken the following morning (see October 22nd), 

 where the tail hangs in cloudy masses like the broken 

 snioke train from a locomotive. In this last picture a 

 large fragment is actually torn off and completely 

 separated from the end of the tail. In the second photo- 

 graph (see the picture for October 21st) the entire comet was 

 brighter, as if the disturbance had added to its light, as 

 also seems to have been the case with the third photograph 

 on October 22nd, for its exposure was much shorter, as 

 flying clouds were obscuring the sky a considerable 

 portion of the time. 



Unfortunately, cloudy weather and moonlight did not 

 permit another exposure until November 2ud, when the 

 comet's tail seemed nearly to have recovered its normal 

 condition, except at its end, where a fragment stuck out 

 almost at right angles, and on November 3rd it was to all 

 appearances again straight ; and thenceforward, though 

 considerable changes of a physical nature were taking 

 place, the comet did not again repeat the phenomenon of 

 October 21st and 22nd. 



In all, up to November 19th, I have secured sixteen 

 photographs of the comet on fifteen different dates. 

 On November 15th two exposures were given of ninety 

 minutes each, in hopes of showing some rapid changes, 

 but the comet was then in a quiescent state, and the two 

 pictures are very much alike. Some of the exposures in 

 the middle of November have been upwards of three hours 

 long. 



Description of the Remainder of the Photographs. 

 I will give here a very brief survey of the different 

 plates, following those already described, and which it is 

 not possible to reproduce here. 



On November 2nd ths tail is about 4' long. It is 

 irregular and somewhat curved. The end is abruptly 



turned through an angle of nearly 90° — a denser portion, 

 about a degree long, projects abruptly from it towards the 

 west. 



On November 3rd the tail is almost straight and some- 

 what broader. The projecting mass is not shown — unless 

 in an unrecognizably altered form. 



On November 6th for 2"^ the tail is straight ; for 2° more 

 it is irregular and wavy ; 6' from the head is a mass, 

 one degree long, entirely independent of the tail. 



On November 7th the tail is nearly straight, but some- 

 what irregular. It is 0^ long. The detached mass is not 

 certainly seen. 



On November iOth the tail is 6° long. Very slender 

 close to the head, then widens out in three distinct fans, 

 the middle one being the main tail. A denser portion at 

 the end almost detached. 



On November 11th the tail is straight but irregular, and 

 in several strands. A denser mass at the extremity. 

 This plate shows a meteor trail parallel with the comet's 

 tail and -1° south of it. 



On November 12th the tail is straight but slightly 

 irregular. A detached mass 2^^ from the end of the tail 

 and south, and 8° from the head. 



On November 13th the tail is short and brushy, with a 

 faint straggling extension to Alpha Canes Venatici. This 

 star is irregularly involved in a condensed mass of the 

 cometary matter. A splendid meteor trail crosses this 

 plate nearly parallel with the comet's tail, and 3'^ north. 

 This trail is sharp and straight and very dense. It widens 

 out as it left the plate, the meteor bursting in the sky a 

 few degrees after leaving the plate. 



On November 14th the tail is somewhat curved and 

 irregular. There are two meteor trails on this plate — one 

 a large one cut across near the edge of the plate ; the 

 other is near Alpha Canes Venatici. 



On November 15th the tail can be traced 10°. It 

 is straight. There is possibly a denser mass at the end 

 of the tail. The two negatives made on this date are 

 essentially duplicates. 



On November 19th the tail is straight ; a thin or weak 

 place occurs in it, nearly isolating the end. 



Cloudy weather since this last date. 



In nearly every one of these photographs there are small 

 "whiskers" — I cannot better describe them — slender 

 thread-like tails — that spring out on each side of the head, 

 and which extend generally from ^° to ^° from the 

 head, and are inclined at a considerable angle to the tail. 



November 27th, 1893. 



IRREGULARITIES IN THE TAILS OF COMETS. 



By A. C. RiNYARD. 



THE beautiful photographs of Brooks' comet, of 

 which Prof. Barnard has kindly sent enlarged 

 copies for reproduction in Knowledge, exhibit 

 most striking irregularities of structure, which are 

 well worthy of close study, for the observation of 

 deviations from assumed general laws has frequently led 

 to fresh discoveries. 



As a general rule, in large comets the tail streams from 

 the nucleus in a direction away from the sun, as if the 

 matter of the tail was repelled by the nucleus and was 

 also repelled by the sun ; and when the tail is curved it 

 falls behind the nalius vector, or line joining the sun and 

 the cometary nucleus, so that the curvature of the tail is 

 concave towards the part of space which has been traversed 

 by the comet, as if the particles of the tail retained their 

 original orbital motion, but being driven into a larger 

 orbit fell behind t he radius vector. 



