THE MINOR PLANET Ml' [Q,II. 2\~ 



It will be seen that the two results agree within their respective 

 probable errors. 



Here, at last, was a minor planet that repaid many years of 

 searching, but it was curious to remark that it was and is still Dr. 

 Witt's only discovery ; one should have expected that the veterans 

 in the field, such as Charlois, Palisa or Wolf, would have secured 

 the prize. At this period minor planets were still largely found 

 by visual observation with ordinary, but. of course, powerful 

 astronomical telescopes. Passing on rapidly, we come to the 

 year 1906, in which no less than 117 new minor planets were 

 announced, every one of which was found by photography. This 

 year was remarkable on three accounts; firstly, for the discovery 

 of the planet since numbered and named 588 Achilles, whose 

 mean distance exceeds that of Jupiter by 0.04; secondly, for the 

 introduction by Dr. Joel Metcalf of the principle of guiding the 

 telescope so that the plate remained approximately at rest with 

 regard to the usual motion of a minor planet, and the stars. 

 instead of appearing as points, are drawn in trails — in this way 

 fainter planets can be photographed; and, lastly, 294 Felicia, 

 which had not been seen since 1891, was refound photographi- 

 cally. Here we have the introduction of another type of minor 

 planet, vis., with a mean-distance nearly the same as that of 

 Jupiter. Since 1906 three other planets belonging to this group 

 have been found, vis., 617 Patroclus, 624 Hector, and 659 Nestor; 

 two members of the group have mean distances slightly less and 

 two slightly greater than Jupiter's, but more remarkable is the 

 fact that they ail travel around the Sun. keeping at an angle of 

 about 6o° from Jupiter, and, so far, supplying four concrete 

 cases of Lagrange's celebrated theorem on the stability- of motion 

 of three bodies situated at the three angles of an equiangular 

 triangle. At the end of 191 1 the minor planets permanently 

 numbered amounted to 714, and out of the 50 new planets 

 announced in that year, no less than eight were found visually 

 by the veteran observer, Palisa. 



As to the present state of their orbits and ephemerides. the 

 Berliner lahrbuch is, as it has been for years, the chief authority, 

 and it lias recently altered the shape in which it prints the 

 ephemerides. Approximate places at four ten-day intervals are 

 given for 563 planets in 1912. that is. practically for all whose 

 orbits are well enough known to permit prediction These ephe- 

 merides are rough, but sufficiently accurate to allow ready identi- 

 fications of objects found. Perturbations will only be computed 

 for planets of special interest. Resides the ephemerides thus 

 published there are a considerable number, in addition, given 

 from time to time in the Astronomische Nachrichten and other 

 astronomical journals by astronomers, who happen to be in- 

 terested in some special planet or group of planets. 



It was by no premeditated design that the observation of 

 minor planets was undertaken at the Union Observatory. It 

 was in April, 191 1, that Mr. Wood took some long exposure 

 (four hours) photographs of Jupiter, in the hope, which was 



