Winterhalter — Personal Equation Machine. 121 



fastened to the cell of the eye-piece on the side nearest the reti-' 

 cule, leaving, however, the entire aperture free. On this ring 

 a glass-plate, 0*1 millimeter thick, was secured with shellac. 

 This plate had a circular opening in its center and was attached 

 in such a position that the edge of the opening passed through 

 the center of the ring. It is obvious that the illumination of 

 the field was now divided into a bright and a somewhat darker 

 part by an arc passing through the center of the field. 



There is seen, then, a part of a bright disk on a half-bright 

 ground, transiting the wires by the motion' of the ocular, 

 as before. By using plates of different-sized openings, disks 

 were obtained corresponding to angular radii of 



16' 2", IV 21", 1' 21", V h", 10". 



The motion in one direction gives the transit of either the 

 preceding or the following limb ; to get the same limb for the 

 reversed motion, it would be necessary to turn the ocular 

 through 180°.' Owing to a limited time, the observations were 

 made only so as to take the mean between errors of preceding 

 and following limbs. 



For a motion corresponding to that of a star of 11° 21' de- 

 clination, the personal equations in observing the limbs, in the 

 order of angular radius above given, were : 



+ s -089, +0 3 '259, +0 S '213, +0 S ']83, +O s -157, 



while for a star the equation in the same position of the tele- 

 scope was found to *be +0 S- 148. Forming the differences 

 limb — star, in the same order, we have : 



— s -059, +0 S -111, +0 S '065, +0 s -035, +0 3, 009. 



The observations in this last investigation are not complete, 

 but it seems to be established that the author's personal equa- 

 tion is different for observation of limb and of star, the differ- 

 ence generally increasing with the increase of the size of the 

 disk observed. 



The advantage of the author's apparatus remains in the fact 

 that with it the circumstances of transit observations can be 

 closely imitated, both as regards the position of the observer 

 and the fulfillment of other desirable conditions. Objections 

 of complication can scarcely be made, as it is not likely that an 

 apparatus of an entirely simple character will be devised to 

 permit a complete investigation of the peculiarities of the 

 personal error. 



