= Comet b 1883. 



= Pons- Brooks Comet. 



= Pons Comet 1812. 



o84 SCIENTIFIC RECORD FOR 1885. 



by Spitaler with the 27-iuch retractor of the Vienna Observatory, while 

 searching for Comet 1858 III, on the morning of May 26, 1884. A period 

 of almost unexampled bad weather followed, and on June 17 and 18 the 

 of nebula was missing. Schulhof seems to think it improbable that this 

 was the comet. Biorsen's Comet, which has a period of about five and 

 one-half years, was due at perihelion in September, 1884, but owing to 

 its unfavorable situation it seems to have escaped observation. 

 Comet 1884 I : A faint telescopic comet was discovered by 



Brooks on September 1, 1883, and it soon proved 

 to be a comet which had been discovered origi- 

 nally by Pons, at Marseilles, on July 20, 1812 — 

 one ofa group, of which Halley's Comet is another member, having a period 

 of about seventy-five years and an aphelion a little beyond the orbit of 

 Neptune. Schulhof and Bossert's careful rediscussion of the observa- 

 tions of 1812 had placed the return to perihelion on September 3, 1884, 

 whereas perihelion passage was actually found to take place on January 

 25. A closer agreement (the error was only y^^ of the whole amount) 

 could hardly have been expected, considering that tbe older observa- 

 tions extended over barely two months. The corrected eleojents make 

 the period 71-56 Julian years. As the second member of this group to 

 return to perihelion, this comet had been looked for with considerable 

 interest, and that interest was subsequently increased, when observa- 

 tion showed the rapid changes suffered by the head in approaching the 

 sun, and the curious fluctuations in the brightness of the nucleus. On 

 the evening of September 22 the comet was described as a faint, round 

 nebula, with a nucleus of the 12th magnitude. On September 23 the 

 nucleus had become as bright as the 8th magnitude. This central mass, 

 according to Schiaparelli, was not a point of light, but had an appre- 

 ciable diameter, and an irregular outline. It now diminished quite 

 rapidly in brightness, and was noted as the 9th magnitude on Sep- 

 tember 29. Another outburst occurred on January 1, 1884, and a care- 

 ful series of photometric observations was obtained by Dr. Mueller, of 

 Potsdam. The nucleus became as bright as a star of the 7th mag- 

 nitude, the change in brightness amounting to more than a magnitude 

 in about an hour and a half. The comet was visible to the naked eye 

 from November 20 to March 3, and at its brightest, with a tail 6° 

 long, it was a fairly conspicuous object in our southwestern sky. The 

 spectrum on the 24th and 27th of September showed nothing unusual. 

 On January 1 Vogel found a continuous spectrum of considerable inten- 

 sity, in which two bright lines were suspected in the yellow. The bands 

 were fainter in the nucleus than in the parts immediately surround- 

 ing it. Vogel concludes from his observations that in consequence of 

 the rapid condensation of the cometary matter into a bright nucleus of 

 several seconds in diameter, a considerable increase in temperature 

 must have taken place, by which the most refrangible band in the comet's 



