214 Messrs. Warren De La Rue, Stewart, and Loewy [Mar. 14, 



might be presumed, ceteris paribus, to be smaller than those observed in 

 ^ the western half, a fact strikingly demonstrated by the above Table. 



Our present object, however, is not to account for the average behaviour 

 of spots, but rather to investigate the causes or concomitants of a de- 

 parture from this average behaviour. We have therefore in all cases made 

 use of the factors given in the above Table as those which, judging by 

 the average behaviour, tend to equalize the areas that pass the various lon- 

 gitudes. We have called this earth-correction, and have limited our dis- 

 cussion to any well-marked behaviour that remains after the earth-correc- 

 tion has been applied. 



6. Let us now divide the whole mass of observations into four portions, 

 depending upon the position of the planet Venus with reference to the 

 Earth or point of view. First, let us take each occasion on which the 

 planet is in the same heliographic longitude as the Earth, that is to say, 

 when the Earth and Venus are nearly in a line on the same side of the sun. 



Let us use five months' observations for each such occasion, extending 

 equally on both sides of it ; thus, for instance, if the planet Venus and the 

 Earth had the same heliocentric longitude on September 30, 1855, we should 

 make use of sun-spots from the middle of July to the middle of December 

 of that year as likely to represent any behaviour that might be due to this 

 particular position of Venus. Let us do the same for all similar occasions, 

 and finally add all the spots thus selected together. We have thus ob- 

 tained a mass of observations which may be supposed to represent any be- 

 haviour due to this position of the planet Venus with reference to the 

 Earth or point of view. 



Secondly, let us now take each occasion on which Venus is at the same 

 longitude as the extreme right of the visible disk, that is to say, 90° before 

 the Earth, and do the same as we did in the previous instance, using five 

 months' observations for each occasion. We shall thus, as before, obtain 

 a mass of observations which may be supposed to represent the behaviour 

 due to a position of Venus 90° before the Earth. Thirdly, let us obtain in 

 a similar manner a mass of observations representing the behaviour of sun- 

 spots for a position of Venus 180° before the Earth* Venus and the Earth 

 being now at exactly opposite sides of the sun ; and fourthly, let us finally 

 obtain, in a similar manner, those observations representing the behaviour 

 of sun-spots when Venus is 270° before the Earth, being now of the same 

 heliocentric longitude as the extreme left of the visible disk. 



These four series of five months each will in fact split up the whole body 

 of observations into four equal parts, the synodical revolution of Venus 

 being nearly twenty months. The following Table exhibits these series 

 after the earth-correction has been applied to each ; it also represents each 

 series reduced so as to exhibit its characteristic behaviour for an average 

 size of spot=1000. 



