500 Proceedings of the Royal Irish Academy. 



movement marked the closing of tlie cnrrent on the chronograph, and 

 the moments when the pendulum gave the audible second-beat. That 

 the last-mentioned interval was constant was found with certainty by 

 observing the two moments, when the coincidences of the beats of the 

 two "assisting-clocks" (observed by the ear) with the beats of the princi- 

 pal clocks on both stations, also observed by the ear, and the coincidences 

 of the contact-signals of the principal and assisting-clocks, registered on 

 the same chronograph, took place. It was found in this way that, in 

 a certain absolute moment, the difference, Leipzig clock-time minus 

 Gotha clock-time, as found by the ear, was always a little less than the 

 same diiference, as found by the chronograph, and the mean deviation 

 of the eight evenings, agreeing very well with each other, was found to 

 he = 0^-282 (/. c, p. 69). It appears from the single results that 

 both, observers (who twice exchanged their stations) agreed per- 

 fectly well in their estimation of the differences by the ear. But as 

 the constant relation of the two time-scales to one another was proved, 

 the personal error must necessarily have changed, if there appeared 

 perceptible changes in the clock-corrections, found in the two different 

 ways. And the following mean differences between the two clock- 

 corrections were found : — 



By Brulins in Leipzig, O^'-iS (o evenings). | By Auwers in Gotha, Os-42 (o evgs.) 

 ,, „ ,, Gotha, -33 (4 evenings). | ,, „ ,, Leipzig, wo (5 evgs.) 



According to Bruhns the difference between the registered and the 

 heard clock-correction in Gotha was + O^'IO different from the one in 

 Leipzig ; according to Auwers, + 0'-33. Above we have seen that 

 the heard second-beats in Gotha came 0''"28 later after the registered 

 ones than in Leipzig. We see now that the difference in estimating 

 registered and heard culminations in Bruhns' case has changed 0^-18 ; 

 in that of Auwers' only 0'-05. 



This result controls very well the direct comparisons. By eye-and- 

 ear was found : — 



18G5. April 12, in Leipzig, B.-A. = + 0^-32 ± 0«-04 



,, Octoher 2, ,, Gotha, ,, = + -11 ± -03 



3, „ „ „ =+0-19 ±0-03 



(B. - A., in Leipzig). 

 ^ (B. -A., in Gotha). 

 = 0^-17. 



We see that it was to Bruhns the change in the eye-and-ear- 

 equation was due, and probably the explanation which the observers 

 themselves give of the phenomenon is the right one. In Leipzig the 

 clock gave double beats (with an interval of about one-third of a 

 second between the single beats), and this had probably distiu-bed 

 Bruhns, so that he perceived the moment midway between the 

 two beats instead of the last one.* It is a pity that the personal 



* The author has found a similar anomaly in himself by taking ti-ansits in . 

 a room, in which a mean-time clock and a sidereal one were placed. 



