G-.—N0..23.

4

REPORT RELATIVE TO MEASUREMENT OF LONGITUDE

The Hutt instrument, and the modes practised for its adjustment, have been fully described in the Report published in the New Zealand Gozette, No. 12, IS7I. The times of transits here were registered by a chronograph, consisting of an ordinary Siemens Register, but fitted with two sets of electromagnets and armature levers; one set of electro-magnets and its armature lever being in circuit with a signal key, upon which the seconds of the chronometer were beaten, and the other with the observer's key for sending signals. By an arrangement of the wires, the instant of a star's transit ■were precisely recorded by the observer, with an embossed dot upon a fillet of paper moving between the rollers of the register, and simultaneously transmitted to Rockyside. The second beats of the chronometer were similarly embossed with the other electro-magnet and armature lever upon the same fillet of paper, but upon a line separated about i-inch from the line of transit dots. The register was started and stopped for each star, taking care to note the exact beat by chronometer of the first beat on starting, and of the last beat after stopping the register. The times of a star's trausits were afterwards read off by transferring the transit dots into the line of chronometer second dots: and thus the exact second and fraction of a second, whenever the observer tapped his signal key, became precisely measured. The signals given from Rockyside were also registered by the Hutt chronometer m the above manner. The personal equation of the observers was determined at the Hutt, by one of them observing the transits of a star over the first two wires of the transit instrument, and the other, of the same star over the last two wires. The times were recorded by chronograph. Each transit was then reduced to the mean wire by the known equatorial interval between each wire and the mean wire. The difference between each observer's independent determination of the star'R transit by chronometer over the mean wire, is the personal equation. The mean of several trials furnished this equation with precision. The personal equation of the telegraphist at Rockyside, is the time elapsing between the instants of the observer giving the signal of a transit occurring, and the telegraphist transmitting the same to the Hutt. It was found, by placing two signal keys in circuit with a Morse's Register. The observer tapped one of the keys at the instant he gave the usual signal of a transit, and the telegraphist tapped upon the other key as when transmitting. The space between the two dots on the fillet of paper, when referred to the length of paper run out by the register in five to eight seconds of time by chronometer, represented, in time, how much later the telegraphist tapped his key after the usual transit signal had been given by the observer. By reference to Appendix D, herewith enclosed, it will be seen that, when the mean electric difference of longitude is applied to the Rockyside absolute longitude, the so deduced longitude of the Hutt Observatory almost identically coincides with its absolute determination. In fact, the absolute or independent difference of longitude, as observed between the two stations, agrees to within 25'fcet of the measured electric difference. That so close an agreement is a mere coincidence, cannot be doubted, as we expected to differ by about three seconds of time. But, as it is nevertheless a positive fact, brought about by two different observers, neither having a previous knowledge that the boon of being able to measure Iheir difference of longitude by the telegraph would ever have been accorded, we beg to state that the longitude of the Hutt Observatory, as derived from sixty-two moon, culminations, is ll h- 39 m-5072 s- East from Greenwich, aud that, according to probability, its error does not exceed one second of time. Since the difference of longitude between the Hutt and Wellington Observatories has been measured by triangulation, we have also been enabled to compare our result with the determinations of our predecessors on this subject. H. M. 8. Chronometric measurement by Captain Stokes, R.N., between Fort Macquarie, Sydney, and Pipitea Point ... ... ... 1 34 1553 Sydney Observatory, West of Fort Macquarie ... ... ... + 022G Difference of longitude, Sydney Observatory and Pipitea Point ... 1 34 17 79 Ditto Wellington Observatory and Pipitea Point — 288 , Ditto Wellington and Sydney Observatories ... 1 34 1491 Longitude, Wellington Observatory ... ... ... ... 11 39 1531 Ditto Sydney Observatory ... ... ... ... 10 05 0040 Ditto ditto as given in Nautical Almanack, 1871 10 04 5986 Difference ... ... ... ... ... „ 054 Captain Carkeek had for many years pursued observations for longitude by lunars, Jupiter's satellites, lunar eclipses, and moon culminations. Unfortunately his calculations have been destroyed by fire, otherwise we would have desired to incorporate his result with ours. He gives the h. m. s. Longitude of the Time Ball, Wellington ... ... ... 11 39 1700 Difference of Longitude, Time Ball and Wellington Observatory ... — 125 Longitude of Wellington Observatory ... ... ... 11 39 1575 The longitude of Otago will now be adopted from that of Wellington ; and, as the longitude of Tauranga will also be speedily determined in the same manner, by Mr. Heale, Inspector of Surveys under the Native Lands Act, there will thus be three points in New Zealand, extending nearly along its whole length, two of which will have been referred to an initial meridian at Wellington. Much being the case, and actuated by the same motives which first induced us to determine the absolute longitudes in our respective Provinces, we beg to submit for the consideration of the Government, that there shall be an initial meridian for the reference of all longitudes in New Zealand, ut Wellington; which, as its capital,