Polytechnic Association. 571 



sons a whole day to convert the chronographic records into numbers 

 and copy them on the blank forms. With the observations printed, 

 the labor is only that of copying, and can easily be done by two 

 persons in two hours. 



In regular transit work, where five or fifteen wires are observed, 

 there will be no necessity for copying the separate wires, as the mean 

 can readily be deduced from the printed fillet, or it may be cut and 

 pasted in the record book. The machine is readily adjusted to indi- 

 cate the same numbers as the clock's face, the type being so set as to 

 point zero-hundredth when the pendulum is at its lowest point where 

 the magnet circuit is completed. In the construction of the apparatus, 

 provision was made for attaching engraved rings to the type-wheel 

 shaft, showing at a glance the time. But these are found not essen- 

 tial, as they would but little facilitate the setting of the type, which 

 is accomplished as follows : The minute type-wheel, which is free to 

 move in either direction, is revolved to correspond to the correct 

 minute. An impression may then be taken and the machine started, 

 when the clock indicates the same, the seconds being readily counted 

 from the beats of the magnet regulating the fast moving train. The 

 whole time for this adjustment need never exceed two minutes. 



In the observation of zone stars, the type may be set to give the 

 integer seconds of mean right ascension, so that the final reduction 

 will always be a small quantity. 



Prof. John Phin — That is exceedingly interesting, and a wonderful 

 achievement of science. The next thing must be to make the tele- 

 scope record its own observations. 



Dr. Van der "Weyde — There is a small error which every observer 

 makes in the time of his observation, which is nearly constant to the 

 individual, and which is called the " personal equation." Prof. Hough 

 has invented an apparatus to determine that personal equation, by 

 which the observer records the time when he sees a ball crossing the 

 field of view, and the ball itself records the actual time. But it will 

 not do for the observer to attempt to correct his personal equation. 

 If he finds that he records the time too late, he must not attempt to 

 record it earlier, or he will be all wrong. He must still make the 

 record when it appears to him to be the exact time ; and then apply 

 the personal equation. Then the telescope has been made to record 

 its own observations. Mr. L. M. Rutherfurd, of this city has taken 

 many photographs of the Pleiades, with his large telescope ; and by 

 means of an instrument constructed specially for this purpose, the 

 relative positions of the several stars can be measured with the utmost 



