16 



PROCEEDINGS OP THE AMERICAN ACADEMY 



made a special series of observations, in which he used both the merid- 

 ian circle and the portable transit instrument on each of eight even- 

 ings, determining the clock error independently with each instrument. 

 The result confirms the correctness of the form of level employed 

 with the meridian circle, and shows that the instrument furnishes 

 trustworthy results for the absolute as well as the relative clock error. 

 The mean correction to be applied to the error found by the meridian 

 circle in order to reduce it to that found by the portable transit in- 

 strument, according to these observations, is -}-0^08 ; the eight sep- 

 arate results are 4-0^20, -f0^06, -]-0^09, +0'.07, -[-0^06, -f-OMl, 

 -|-0\09, -|-0^-05, the first having a weight of one third. As the mag- 

 nifying powers and the reticules used with the two instruments differ 

 materially, the amount of the correction is not surprising. 



The results for the error of the sidereal clock obtained from the 

 observations with the meridian circle near the time of the transit are 

 exhibited in Table I. The first two columns contain the date of the 

 observations in mean solar days and tenths, and the sidereal time, to 

 hundredths of an hour, for which the error was determined. The 

 third column gives the number of stars on which each result for clock 

 error depends. The next two columns give the amount by which the 

 clock was slow at the time of each set of observations, and the corre- 

 sponding error for noon of December 6, corrected by means of the 

 hourly rate -)-0'.023. The last two columns contain the values of 

 the instrumental constants n and h (angle at pole, and inclination of 

 axis). 



TABLE I. — Observed Clock Errors. 



The mean result for noon of December 6 is -j-S™ 22'.33. Re- 

 ducing this to the result to be expected from the portable transit 

 instrument, by adding -|-0'.08 as above, we have -j-^"" 22'. 41, with an 

 hourly increase of -[-^'•023. 



