96 Telegraphic Determination of the Difference of 



chronograph, and correcting them for the clock errors as 

 determined from the star observations, the difference 

 between the times will represent the difference of longi- 

 tude viinus the time of transmission, plus the difference 

 of personal equation of the observers. On the other hand, 

 the Hobart Town results will exibit the difference of longi- 

 tudc; plus the time of transmission, plus the difference of 

 personal equation. On taking, then, half the sum of the two 

 quantities, we shall get the difference of longitude freed 

 from the transmission time, but still affected with personal 

 equation. And half the difference of the quantities will 

 give the time of transmission. The effect of personal equa- 

 tion could be eliminated by the observers exchanging their 

 stations ; but as that would have been attended with great 

 inconvenience, the difference of personal equation was 

 directly obtained on several occasions during Professor 

 Harkness's visit to Melbourne. The method adopted for 

 this purpose was for both observers to determine the error 

 of the Melbourne transit clock on the same evening, select- 

 ing the stars in such a way that the mean epoch of each 

 obsei-ver would be so nearly alike as to give the personal 

 equation free from the influence of the rate of the clock. 

 The following is an abstract of the results : — 



COMPUTATION OF THE PEESONAL 



EQUATION 





Date, 



Melbourne 



Mean Time, 



1874 & 1875. 



i 



o 



1 



Mean of 



Times 



of the 



Corrected 



Transits. 



Observed 



Clock 

 Corrections. 



Adopted 



Correction 



for Clock 



Rate. 



H-W 



Reduced to 

 the same 

 Epoch. 





Product. 



d. h. m. 







h. m. 



S. 



per diem. 









Nov. 17 9 6 



H 



5 



51 



- 30-921 



s. 

 - 0-26 



s. 

 + •125 



55 



6-876 



9 25 



W 



6 



1 10 



31-049 











Feb. 23 8 15 



H 



7 



6 27 



32113 



+ 0-36 



+ •171 



77 



13-167 



8 34 



W 



7 



6 46 



32-280 











26 8 43 



H 



6 



7 7 



31-078 



+ 0-30 



+ •171 



66 



11-286 



8 35 



W 



6 



6 59 



31-251 











27 8 20 



H 



6 



6 47 



30-718 



+ 0-29 



+ -242 



60 



14-520 



8 25 



W 



5 



6 52 



30-959 











Adopted Personal Equation H-W 



268 } 45 -848 



+ -178 



