JtUy 7, 1881] 



NA TURE 



22' 



I HAVE made some sketches of this comet, and have 

 taken some photographs with the 3-foot reflector. Par- 

 ticulars of the latter may Ije useful. 



On the night of June 24 the comet, which was very 

 brilliant, presented the appearance of Fig. i ; the nucleus 

 very bright and some 6" in diameter, and not in the centrt- 

 of head. Photographs with two minutes' exposure gave 

 a decided impression on the gelatine dry-plate ; with 

 twenty-one minutes' exposure the image was very dense, 



Fig. i.-Ju 



and the small bright tail that proceeded from the nucleus 

 comes out well, but owing to the rapid motion in declina- 

 tion the image of the nucleus appears as a trail some 

 quarter of an inch long. 



On June 25 the appearance of the comet was altered, 

 the club-footed mass of light had disappeared, and the 

 nucleus presented a rayed appearance. 



Photographs were taken with similar results to those 

 obtained on the 24th, but a dense image of the nucleuj 



was got with one minute's exposure. The intensity of 

 light must quite equal that of a seventh magnitude star. 

 The small bright tail was still very apparent, but between 

 it and the edge of the large tail proper there was a de- 

 cided dark space on the / side. At I3h. 35m. the/ side 

 was noted to be much the brightest ; this change must have 

 taken place very suddenl)', as it had been specially noted 

 jast before as being the faintest siJe of the tail. Fig. 2 



was taken before this was noticed. Cloudy nights inter- 

 vened till the 29th. I had in the meantime fitted a fine 

 screw to the plate-holder, and found that by giving this 

 screw a certain calculated part of a turn every half minute 

 for twenty minutes, I got a fair negative (I beg to forward 

 this for your inspection) without any of the distortion 

 caused by the motion in declinaticin. 



The comet was observed to have changed to a much 

 more symmetrical form (see Fig. 3). The conditions under 

 which the photographs were ta'en were not very favour- 

 able : the mirror and fiat were not at the best as regards 

 polish, and the plates were about two years old. 



A. AiNSLlF. COMMIN 



Thf. comet engaged the attention of the Paris Academy 

 of Sciences at their sitting last Monday week, and we 

 give the following extracts from the papers communi- 

 cated. 



Admiral Mouchcz writes as follows: — "This comet, 

 which was observed for the first time seventy-four years 

 ago by an Italian monk on September 9, 1807, was 

 observe i by Pons eleven days afterwards at .Marseilles 

 on the 20th, and remained visible till March 27, 1S08; 

 during this long period it was possible to make a large 

 number of observations, so that liesscl could for the first 

 lime calculate its elements; and he found that the 

 period of its revolution mu-t be comprised between 1404 

 and 2157 years, and was probably 1714 year?. The cal- 

 culations being revised and account taken of new per- 

 turbations, a period of 174 years was arrived at. The 

 observations made during its second appearance will 

 doubtless render it po-sible to determine the causes of 

 perturbations or the errors of calculation and observation 

 which have rendered its present return so unexpected. 



" M. Tisserand has called my attention to a comet, not 

 catalogued, but cited in Struyck's work, ' V'ervolg van de 

 Beschryving der Staatstcrren' (Amsterdam, 1753), which 

 appears to have been seen at the Cape of Good Hope in 

 1733, jubt seventy-four years previous to 1S07 ; the want 

 of precise observations, doubtless, did not allow of calcu- 

 lating the elements ; but the identity of the period and 

 the comet's appearance in the southern hemisphere lead 

 us to suppose that it is the same comet as we observe 

 now, and which, from some cause difficult to conceive, 

 seems not to have been observed in Europe after its 

 passage through perihelion. Perhaps the Dutch, to whom 

 the Cape of Good Hope then belonged, will find in their 

 archives some documents which will enable us to utilise 

 this old observation, to which I have invited the attention 

 of M. Oudemans, the learned and able astronomer of 

 Utrecht." 



