1886.] Observations respecting Hallei/s Comet* 61 



Jupiter, which he computed would delay the return hy about 

 a twelve- month; had he taken account of the action of the 

 planet Saturn the prediction would have been 100 days later, 

 "■pnd would have agreed to within a few clays of the observed 

 return to- the Perigee : at its last appearance in 1759, 

 Clairavt computed that the planet Saturn would retard it 

 by 100 days, and Jupiter by 511 days, a result agreeing 

 within about a month of the truth. But to return to our 

 own £$&£fe in which we have the benefit of very superior 

 instruments, together with numerous and well appointed 

 observatories; "what are now the fruits ? 3J In the year 

 1822, it was found that the map of planet Venus had been 

 assumed too small by about T V and that an equation going 

 through its period in 250 years had been omitted ; as late as 

 1833 the mass of the planet Jupiter was corrected from toVt 

 to ttfet of the mass of the Sun, &c. &c. &c. In 1824 and 

 from that time up to the present, strong suspicions were and 

 arc entertained of the existence of an aether instead of a 

 vacuum, which, extending throughout the solar system, there- 

 by retards the planets in their orbit, (but consider gentle 

 reader, that if this aether does exist its density is eight hun- 

 dred times less than that of atmospheric air S) requiring how- 

 ever many more observations than we at present possess to 

 decide the point. Now in the prediction of the return of 

 the Comet which is just departing (to the most part of us 

 for ever 1) the effect of the aether was computed to accelerate 

 the return by 13 days, is it then to be wondered at, that a 

 discrepancy of half this amount should occur in a computa- 

 tion clogged with difficulty on every hand, and tedious to the 

 last degree — one which requiring the utmost mathematical 

 knowledge and skill has found a dozen individuals only com- 

 petent to undertake it ? It will be as well now to conclude 

 this subject by exhibiting the elements of the orbit of this 

 Comet as predicted by Pontecoulant, and the same com- 

 puted by myself* from observations made at this Observa- 

 tory, thus : 



* I take this opportunity of acknowledging my obligations to Goday 

 Vencata J uggarow, who rendered me very great assistance in the com- 

 putation. 



