The point of departure in Sydney harbour was Fort Macquarrie, which was assumed to be in longitude 151 14′ 00″ E. Pipitea Point, in Wellington Harbour, was placed in longitude 174° 47′ 53″ E., difference being 23° 33′ 53″, or 1h. 34m. 15.533s.

It has been since ascertained that there was error in this assumed longitude for Fort Maequarrie, and that' Fort Macquarrie is 2.63 seconds E. of Sydney Observatory.^*

The longitude of Sydney Observatory was taken as 10h. 04m. 53.9s. E. Wellington Observatory is 3300.2 feet W., by measurement from Pipitea Point, or 2.88 seconds.

These data thus gave result:—

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This longitude is at present used at the Observatory. True time is there gained and corrected for this constant error 9m. 09.183s., so that the clock which drops the time ball shows always the same time as a clock stationed at 11h. 30m. 00s. E. There is this manifest advantage in this plan: a shipmaster has only to note the difference of his chronometer from 12h. 30m., when the Wellington ball drops, to gain a Greenwich date; and so, observing from time to time, to gain the rate of his chronometer.^†

In the early part of this year a communication was received from Dr. Russell, Astronomer Royal at Sydney, proposing to interchange signals between Sydney and Wellington. At an arranged time, at the ending of each fifteen seconds in five minutes, a key was pressed down, thus giving twenty signals; and, after an arranged interval, twenty similar signals were received from Sydney.

Dr. Russell gives this as the result:—

I have no hesitation in saying that the signals from Wellington to Sydney are of more value than those from Sydney to Wellington, and that

the former value is more likely to be true than the latter, for these reasons: I sent the signals from Wellington, and the evidence of all in the Observatory was that the key was pressed down synchronously with the fifteenth-second beats of the clock. The signals from Sydney were received by an assistant, whose cry at the movement of the flash, as the Sydney key was pressed down, was compared by me with the clock beats. Thus the second process passed through two observers. It is also vastly more difficult to receive than to send. It may be certainly presumed also that the Sydney observers were more practised in the work than those at Wellington, to whom the work was new. But the difference thus gained thoroughly establishes that obtained by the chronometers of the “Acheron” and “Pandora.”

*Fort Macquarrie Pipitea Point* 1h. 34m. 15.533S. *Sydney Observatory, 2.63 E. of Fort M. Wellington Observatory, 2.88 W. of P. Pt.* 1h. 34m. 15.99.49s.

The difference between the two values is only half a second; and if, as I think should be done, that value be allowed for superiority of the signals from Wellington to Sydney to those of the reverse way the two values will be nearly identical.

The value now given for the longitude of Sydney Observatory is 10h. 04m. 47.32s. This new value would give for that of Wellington Observatory 11h. 39m. 02.6s.

The value of Sydney Observatory, however, as gained from the Observatory of Melbourne is 10h. 04m. 50.61. This value gives for Wellington Observatory 11h. 39m. 05.893s.^*

Major Palmer's value, gained by comparison of time difference between Wellington and Burnham (Burnham longitude being fixed after several months' observation), is 11h. 39m. 4.81s.^‡

These longitudes are therefore:—

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Confessedly no problem is more difficult than that of obtaining an absolute longitude by observation. Even with the instruments at the Royal