Tioyal Astronomical Society. 1 -tS 



Professor Mitchell has found it convenient to use, for the seconds- 

 record, a pen or style different from that which is used for the ob- 

 servation-record. He does not mention whether he uses for the 

 seconds-record a battery different from that used for the observation- 

 record ; but this appears necessary to prevent the confusion which 

 might arise in the register on making observations exactly at the 

 second of time ; for the completion of the battery-circuit by one wire 

 would probably interfere with the efficiency of the circuit through 

 the other wire. 



The Astronomer Royal does not hesitate to express his preference 

 of Professor Mitchell's form of register to Dr. Locke's. 



The practicability of this method of recording observations being 

 fully established, it then becomes an important question for the ob- 

 serving astronomer, whether this method is or is not more accurate 

 than the usual method of observing by the combination of eye and 

 ear. The question is, really, whether the connexion between the 

 nerves of the eye and of the finger is or is not closer than that between 

 the nerves of the eye and of the ear : it is purely a physiological 

 question, which can be settled only by experience. Professor Mitchell 

 has investigated it in the following manner. Extracting from the 

 printed Greenwich Observations a number of transits of a Coronae 

 and comparing their intervals \vith the intervals as established from 

 observations of the pole-star, he has obtained a measure of what may 

 be called Greenwich Irregularities. Using the same process for the 

 observations recorded by the Galvanic Register, he has obtained a 

 measure of Cincinnati Irregularities. The magnitude of the latter is 

 only about one-fourth of that of the former. The Astronomer Royal 

 suggested that a portion of this difference might be owing to the 

 difference in the state of the two atmospheres, the atmosphere of 

 England being perhaps com])aratively unfavourable to accurate ob- 

 servation. The result of Professor Mitchell's comparison is, however, 

 very encouraging as regards the probable success of the method. 



One important advantage of this method would be the contraction 

 of the time of observing a transit. Instead of using wires 12^ or 15' 

 apart, intervals of 2* will be amply sufficient. Advantage may be 

 taken of this, either for the observation of numerous objects, or for 

 observation over numerous wires. One inconvenience of the method, 

 however, is, the trouble of translating the graphical registers into 

 numbers. Another inconvenience, of great weight, is the extent of 

 recording surface that will be required, unless the recording ma- 

 chinery be very frequently disengaged, and its records (to a certain 

 degree, not essentially injurious, but troublesome) be rendered dis- 

 continuous. In the Royal Observatory of Greenwich it is by no 

 means uncommon to have trains of interrupted observations ex- 

 tending over twelve hours, or even a longer time, at once. An 

 unbroken series of time-marks of 12 hours in Dr. Locke's method, 

 allowing 1 inch to each second, would require 3600 feet of paper 

 fillet ; in Professor Mitchell's method, allowing i inch for each second, 

 and Jq. inch between successive lines of dots, it would require a 

 sheet of 1440 square inches of paper. 



Phil, Mag. & 3. Vol. 36. No. 241. Feb. 1850. L 



