298 



REPORT — 1851. 



in which the priming-stick was launched to a surprising height in the air. 

 The final junctions between the batteries and the priming cartridge wires 

 were made by brass binding screws, leaving but one point of broken contact 

 to be made good, namely that at the firing chronograph. 



Previous to the two chronographs being brought out and landed on Dalkey 

 Island, they were both timed by the seconds' clock in Dublin as before. 

 The following is a record of these timings. 



The chronograph was wound and let run down a known number of com- 

 plete revolutions in each experiment, and the seconds and fractions in the 

 time taken to do so noted by reckoning the beats of the seconds' clock and 

 observing the place of the pendulum over the graduated arc at the moment 

 of completing the revolutions. 



Eight experiments were made in each case, in four of which the writer 

 started and stopped the chronograph and William Mallet observed the clock, 

 and in the other four he started and stopped and the writer observed the clock. 

 Then, averaging the whole, the personal error was got rid of in each case. 



The personal equations for both observers were also arrived at from these 

 experiments, but require repetition before a result applicable to the main 

 purpose of these experiments themselves can be had. 



The following table gives the results of the experiments for timing of 

 Wheatstone's chronograph, which was that used at the firing end of the range, 

 and Sharp's chronograph at the transit or observing end. 



Wheatstone's Chronograph. 20th Sept. 1850. 

 Eight revolutions made in all cases. 



Clock 



' observed by 



Wm. Mallet. 



Clock 

 - observed by 

 Robert Mallet. 



:4"-798 time of one revolu- 

 » . 4'"*798 



tion of large dial. One division of the large dial is therefore = 



0"-3991 



30 



12 

 =0"-0133 



=0"'3991, also equal one revolution of the small dial, and ■ 

 equal one division of the small dial. 



The personal equation deducible from the above is as follows. All Wil- 

 liam Mallet's observations are of shorter times than mine, and assuming the 

 chance of error equal in each case, 



Wm. Mallet's four observations. R. Mallet's four observations. I 



Exp. 



1. 38-0 



2. 37-5 



3. 38-0 

 4.. 38-25 



4)151-75 

 Average 37-937 

 This divided by 8 revolutions = 

 4"-74'2 = time of one revolution of 

 large dial. 



Exp. 5. 38-75 



6. 39-0 



7. 39-0 



8. 39-0 

 4)155-75 



Average 38*937 

 This divided by 8 revolutions s=" 

 4."-867 = time of one revolution of 

 large dial. 



