Chase.] 470 [Oct. 3. 



RECENT CONFIRMATION OF AN ASTRONOMICAL PREDIC- 

 TION. 



By Pliny Eakle Chase, 



Professor of Physics in Haverford College. 

 (Bead before the American Philosophical Society, October 3, 1873.) 



In a communication to the Society on the 2d of May last,. I gave cer- 

 tain harmonic indications of "a possible unknown planet, planetoid 

 group; or other seat of solar and planetary perturbation" at about ^ of 

 the "Earth's mean distance from the Sun.* I also suggested that Wolf's 

 supposed sun-spot period of twenty-seven days "might be readily 

 explained by the perturbations and transits of a planetoid or meteoric 

 group, at a distance which would complete the terrestrial harmonic 

 series." If there is any such source of perturbation, there should be 

 not only maxima and minima of sun-spots at average intervals corres- 

 ponding with the period of solar rotation, but there should also be sub- 

 ordinate maxima and minima at intervals of a half-rotation, inasmuch as 

 the tidal influence would be exerted simultaneously at opposite extremi- 

 ties of the same solar diameter. 



During my summer holidays I was enabled, through the courtesy of 

 Prof. Joseph Winlock, Director of the Observatory of Harvard University, 

 to examine observations of sun-spotted area, extending over a period of 

 nearly five months. They furnished indications of such disturbances as 

 I have described, but the period of observation was so short that I did 

 not regard them as conclusive. 



On my return to Philadelphia, I found in Nature, of July 17, an 

 abstract of a communication to the Royal Society on June 19, by Messrs. 

 De La Rue, Stewart and Loewy. Those eminent observers adduce evi- 

 dences of a tendency in sun-spots "to change alternately from the north 

 or positive to the south or negative hemisphere, and vice versa,'' 1 and they 

 attach special significance to the fact "that the two outbreaks are at oppo- 

 site ends of the same solar diameter.'''' These conclusions are based upon 

 three sets of observations, taken in three different years, and extending 

 over periods, respectively, of 145, 123, and 139 days. Their lowest 

 approximate estimate of the mean interval between two maxima of the 

 same sign, is 22.25 days ; the highest, 28 days ; "the most probable mean 

 value, 25.2 days." The interval between two maxima of the same sign 

 and originating at the same axial extremity, would of course be twice as 

 great. 



There seems, therefore, to be conclusive evidence of some disturbing 

 force, revolving around the Sun in a period approximately equivalent to 

 two solar rotations. The mean radius vector of such a disturbing force 

 should be : 



According to Sporer 2G3 



" Carrington 205 



Faye 266 



*Ante p. 238 ; see also New York Tribune. May 2. 1S73. 



