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Volume 7, 1874
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Memorandum on the Longitude of Wellington Observatory.

1.

“On the Hot Winds of Canterbury,” by Alexander McKay, of the Geological Survey Department. (Transactions, p. 105.)

Captain Edwin thought the winds described must be of a local character, and that they might not be from the north-west, but receive their direction from the shape of the mountains.

2.

“Notes on certain disputed Species of New Zealand Birds,” by Walter L. Buller, D.Sc., F.L.S., C.M.Z.S., etc. (Transactions, p. 211.)

3.

“Memorandum on the Longitude of Wellington Observatory,” by Captain Nares, of H.M.S. “Challenger,” with enclosing letter by Dr. Hector, F.R.S.; communicated by the Hon. the Colonial Secretary.

Colonial Museum, wellington, 9th september, 1874.

Sir,—I have the honour to forward a memorandum relative to the longitude of Wellington, which has been addressed to me, as officer in charge of the Observatory here, by Captain Nares, of H.M.S. “Challenger.”

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It is satisfactory to find that the longitude which is at present used for finding the local New Zealand time is within 81 of a second of that which is given by the observations now communicated by Captain Nares as the result of the investigations of the officers of H.M.S. “Challenger.” Thus, the chart longitude at present used to find the local Wellington time, in accordance with a decision arrived at by the Board appointed in 1870 (App. to Journ.

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H. M. SEC.
H. of R., D—27), is 11 39 11·53
The longitude for the same, deduced from the longitude now given by the “Challenger” from the Wellington Observatory, is Pipitea Point, E. Pipitea Point, E. + 2.88 11 39 10·72
Defference ·81

It is true that the longitude, as determined by the absolute observations of Chief Surveyors Jackson and Thomson (App. to Journ., 1871, G—23), would appear to be 11h. 39m. 18.19sec., but this longitude has never been accepted in the practical working of the Observatory, as it would involve the serious consequences pointed out in the latter part of Captain Nares' memorandum; and as it differs from all chronometric measurements, which, in the opinion of the Astronomer Royal and Professor Ellery, are more reliable than absolute determinations, owing to the defects in the lunar tables.

As to Captain Nares' remarks relative to the method at present adopted of giving the time-ball signals, I venture to differ from his conclusion on the subject, as he appears to be under a misconception as to the method which is in use. When a time-ball drops in any part of New Zealand, a ship's chronometer, if set, as is usually the case, to Greenwich Mean Time, should show 12h. 30m., and any difference from this will be the error, fast or slow, on Greenwich Mean Time. The local time at any port can at once be obtained by applying the difference between the chart longitude for that place and 11h. 30m. E., or 172°30’ E. of Arc. This appears to be as simple a method, both for rating and correcting chronometers, as can well be contrived, and is, besides, in accordance with the practice adopted round the coasts of England and Scotland, where Greenwich time, and not the time at place, is indicated by the local time-balls.

I cannot therefore concur in the suggestion that, in giving the time-signals in different parst of the colony, local mean time at place should be adopted.

As the correct longitude of Wellington Observatory, being the initial longitude for New Zealand, will be required by the officers in charge of the observation of the transit of Venus, I may state that the longitude, as determined from the difference between Sydney and New Zealand, measured by Captain Stokes—and corrected for the error since ascertained for the

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position of Sydney—is, in all probability, most correct, having been taken under very favourable circumstances. Thus:—

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H. M. SEC.
Melbourne Observatory E. 9 39 54·80
Difference to Sydney, by telegraphic observation E. 24 55·81
Fort Macquarie E. 2·63
Difference to New Zealand E. 1 34 15·53
Probable true longitude of Pipitea Point 11 39 8·77
Wellington Observatory W 2·88
Probable true longitude of Wellington Observatory 11 39 5·89

This is about two seconds less than the longitude given by Captain Nares, but I think it should be preferred, as he himself points out that the “Challenger” observations were not taken under the most favourable circumstances.—I have, James Hector.

The Hon. the Colonial Secretary, Wellington.

Memorandum for Dr. Hector, F.R.S.

The meridian distance between the usual observatory place at Sydney (viz., the Flagstaff at Garden Island) and the Cathedral at Wellington, by the “Challenger's” chronometers, was found to be 1hr. 34min. 15.47sec.

In order to make this meridian distance of use, to determine the longitude of the Observatory at Wellington, it is necessary to know the exact position of that Obsevatory with reference both to the Cathedral and Pipitea Point. Unfortunately neither of these positions are given on the plans furnished us by the local surveyor, so that we are obliged to have recourse to the small plan of the port published by the Admiralty; and it was also unfortunate that we were unable to observe at Pipitea Point (the position selected by Captain Stokes), but now this has become the railway terminus the vibration of the ground renders it impossible to obtain accurate observations in this locality, and, being at the time unaware an Observatory had been established at Wellington, we chose the Cathedral, as being a building likely to be permanent, and in the vicinity of which good observations might always be obtained.

To compare the meridian distance obtained by us with that of Captain Stokes, both are referred to the Observatory at Sydney and Pipitea Point.

Captain Stokes' meridian distance is—

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H. M. SEC.
From Fort Macquarie, Sydney, to Pipitea Point 1 34 15·53
Sydney Observatory west of Fort Macquarie 2·63
Sydney Observatory to Pipitea Point 1 34 18·16

The “Challenger's” meridian distance is—

From Garden Island Observatory δ to Cathedral, Wellington 1 34 15·47
Sydney Observatory west of Garden Island Observatory δ 5·73
Sydney Observatory to the Cathedral, Wellington 1 34 21·20
The Cathedral west of Pipitea Point ·87
Sydney Observatory to Pipitea Point 1 34 22·07
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Taking the mean of these two results:

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H. M. Sec.
Captain Stokes' meridian distance 1 34 18·16
"Challenger's ditto 1 34 22·07
2) 40·23
Mean 1 34 20·11

The meridian distance between the Observatory at Sydney and Pipitea Point will be 1h. 34m. 20.11sec., and this is probably within half a mile of the truth. It is, however, possible that, in taking the arithmetic mean of these two meridian distances, we are giving our own too great a value, as, owing to bad weather and the delay consequent on sounding for the telegraphic cable from Sydney to New Zealand, twenty-one days elapsed between our observations at Sydney and Wellington.

If Captain Stokes ran his distance directly from Sydney to Wellington, as he probably did, he would certainly have obtained observations at the two places with a less interval of time, and his distance would therefore be of much more value than ours. In the absence of precise information as to how his distance was obtained, we have assumed for the present the two results to be of equal value. The Observatory at Wellington is said to be 2.88sec. west of Pipitea Point, the meridian distance therefore between the Observatories at Sydney and Wellington will be 1h. 34m. 17.23sec.

The next point to determine is the absolute longitude of the Observatory at Sydney. That longitude was determined by Mr. Scott by absolute observations, and he made it 10h. 4m. 47.32sec. E. of Greenwich. Lately telegraphic time signals have been exchanged between the Observatories of Melbourne and Sydney, and the meridian distance found to be 24m. 55.81sec. The longitude of the Melbourne Observatory, as determined by Mr. Ellery, is 9h. 39m. 54.8sec. E. of Greenwich. By absolute determination, therefore, the meridian distance between the two Observatories is 24m. 52.52sec., or 3.29sec. different from the result obtained by telegraph, which result is necessarily correct. It is therefore evident that either one or both of the determinations for absolute longitude must be in error, and this error is most probably in the Sydney determination, as better instruments were used at Melbourne. Assuming, then, for the present that the longitude of the Melbourne Observatory is correct,

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H. M. SEC.
The longitude of Melbourne Observatory is 9 39 54.80 E.
Sydney Observatory east of Melbourne 24 55.81 E.
Wellington Observatory east of Sydney Observatory 1 34 17.23 E.
Longitude of the Wellington Observatory 11 39 07.84 E.

The longitude of the Observatory at Wellington may therefore, for the present, be considered as 11h. 39m. 7.84sec. E. of Greenwich. Opportunity

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will, no doubt, present itself of verifying and correcting this as soon as the telegraphic cable is laid between New South Wales and New Zealand.

It is perhaps as well for us to point out in this paper that the present method of dropping the ball at Wellington, which method is, we understand, adopted over the whole of the New Zealand islands, is liable to lead to grave error.

It must be evident that in order that a time signal should be of use for purposes of navigation, that signal should be given on a principle which admits of its being readily applied to the charts on which the seaman plots the position of his vessel. These charts are all graduated on a certain system, and on an assumed longitude of a selected position on each sheet, which longitude is the subject of most careful attention at the Hydrographic Office, and every longitude on, or adjacent to, one well-determined position is made to coincide with that position. Thus, every longitude on the published chart of New Zealand is relatively correct with the given longitude of Wellington. Now, the longitude of Pipitea Point on the chart is 174°47°53° E., while the ball at the Custom House has been dropped at an assumed time of 11h. 30m. from Greenwich, and this assumed time has been taken as being 9m. 15.75sec. west of the Wellington Observatory, or 9m. 18.63sec. from Pipitea Point; therefore the ball was dropped as if Pipitea Point was in longitude 174° 49° 39° E., or 1 3/4 miles east of the position given on the chart. A ship, therefore, rating her chronometers by the ball at Wellington would always be 1 3/4 miles west of the position plotted on the chart, and this might be of serious moment.

This difference, no doubt, has been caused by the desire of the colony to adopt one mean time for the whole of the islands, an object the advantages of which few people will dispute, and in doing which an error of a minute of time in the absolute longitude assumed as the mean is of no moment. Very different, however, may be the results when that empirical time is used as a standard for seamen. Then every second becomes of consequence, and it is necessary to be most careful that errors are not allowed to creep in. Probably the only way to avoid this is to give a time signal at a certain specified moment (say noon or 1p.m.) mean time at place, which time can always be ascertained correctly, leaving the seaman to apply the difference of time, as denoted on his chart, between the place he is at and the meridian of Greenwich. By this means he will always be certain that the astronomical position of his vessel ascertained by him at sea is relatively correct with the adjacent coast, both being laid off on the same chart.

G. S.Nares, Captain R.N.

Captain Edwin thought that the time-balls should drop to local time, as

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otherwise seamen would have to refer their observations to an imaginary meridian.

Mr. George did not see what they could want with observations, as when a seaman is in port he must surely know where he is.

Dr. Hector said the practice at present adopted was the same as round the British coast, where the time signals for shipping are given in one uniform time, being that of Greenwich, and not in the local time for each place. Besides, the inconvenience to the public would be very serious if local time were again resorted to.

The President thought the present system was certainly the best, as the object was to give navigators the correct Greenwich time. He did not see for what purpose they could require local time, but it could be easily obtained by referring to the longitude of the port they were in, as given on the chart, and calculating its difference from the average longitude of 11h. 30m. east, which has been adopted as the mean time for the whole of New Zealand.

4.

“Notes on New Zealand Whales,” by James Hector, M.D., F.R.S. (Transactions, p. 251.)

In this communication the author described the skull of a calf of Neobalœna marginata, and some other interesting forms, which he exhibited, and particularly the skull and some other portions of the humpback whale (Megaptera, Gray), which he considered to be the same whale as recently described by Dr. Gray as a Balœnoptera, or finner whale. He also gave an account of a sulphur-bottom whale, seventy feet in length, the skeleton of which he had secured in Port Underwood, and which he considers to be the true Physalus, or finner whale. The present list of whales, he thought, would have to be very much reduced in the number of species, and even genera.